When I was growing up, my otherwise frugal father leased a new car every three years. He claimed that, as a financial planner, his clients expected him to look successful, which meant driving a nice, late-model car. He reasoned that nobody would take investment advice from a financial planner who drove a 14-year-old Datsun Bluebird. His message to me was clear: Invest in your career.Even as a kid, I had my doubts about Dads logic. Spending money to make money never sat well with me, especially when there was no direct relationship between the purchase and the ROI. (I also suspect Dad hated long-term auto maintenance and he used his clients expectations as a convenient fig leaf.)Considering my early skepticism, it should come as no surprise that I tend to under-invest in my career as an adult. But avoiding financial investments that could advance my professional ambitions has cost me opportunities, which has sometimes led to me overspending as an over-correction.Figuring out the appropriate level of career investments is never going to be easy, but the following guidelines can help you decide if a financial outlay is worthwhile.When it makes sense to spend moneyCompared to trying to suss out which opportunities are worth the money and which should get a pass, just saying no to all professional investments is an easier call.This is why I have consistently under-invested in my career. Im more comfortable saying no to everything rather than trying to figure out a good use of my money. But there are times when investing money into your career is the right thing to do. These include:When you can increase the value of your timeYou are probably well aware of the numerous online calculators that can help you pinpoint the dollar value of your time. Productivity experts often recommend using these types of equations to help determine what tasks you can outsource, since hiring an assistant can free up your time to focus on more lucrative tasks.But outsourcing is not the only way you can make your time more valuable. Getting certification or other education can often lead directly to higher pay, which literally means your working hours are worth more.Similarly, you might also spend money to ensure you bring your A-game to work. For example, a nervous flyer who is traveling to make a major presentation might upgrade their flight to feel more comfortable. The additional cost could be worth the money if it means feeling calm and ready for the meeting, instead of frazzled and stressed.One could argue that my fathers car-leasing habit helped increase the value of his time. By keeping cars no longer than three years, Dad saved himself the time and brainspace he would have needed to keep an older, paid-for car humming along.When you can expand your networkA large and diverse network is one of the best ways to open doors to new jobs and opportunities. This is why career investments that widen your network can be a great use of your money.Whether you are considering attending a conference, joining a professional organization, taking a class related to your industry, or joining a community association, the potential cost of these investments can often be worth it because of the professional connections you will make.When you should save your moneyNot every career investment is a good reason to break out the credit card. While it can be easy to talk yourself into spending money to increase your income (just ask anyone who has been suckered into multi-level marketing), its helpful to remember that not all investments will benefit your career.Heres when you should think twice about putting your money into a career investment.When youre substituting money for actionAnytime we dont know how to do something, it can be very tempting to throw money at the problem. For example, lets say a small business owner is struggling to build their clientele. They hear about a $2,000 seminar that promises to help them scale up their marketingand they get excited about using it to increase their client base.The seminar itself might be a very useful opportunity. But the entrepreneur could improve their situation in a number of free or cheap ways before spending two grand on a seminar. The high cost of the seminar can trick the business owner into thinking that they are taking significant action, but its instead allowing them to avoid the work they need to do. And its putting them in a worse financial situation.When you feel pressuredThere are a number of ways you might be pressured into investing money in your career. The more overt (and easier-to-avoid) version is the urgent sales pitch. These kinds of time-bound sales are common in every industry, including career development. This kind of pressure looks like a ticking clock counting down minutes left before the incredible career coaching deal is gone forever.While that sense of urgency can feel a bit stressful, committing to a 24-hour waiting period before purchasing anything can help you avoid succumbing to this kind of pressure.The more subtle pressure feels more like wanting to fit in. For example, if your coworkers all look like they could walk the runway, you might spend more than you can comfortably afford on your work wardrobe. Or you might attend conferences or weekly happy hours to look like a team player, even though you dont want to be there.If youre feeling this kind of pressure, remind yourself of what you really want from your career and your budget. Having clarity about your own values makes it much easier to resist pressure.You work hard for the moneyInvesting in your career can potentially give you a leg upor waste your money.You can figure out which investment is which by asking yourself which opportunities increase the value of your time or expand your network, and which ones allow you to substitute money for action or make you feel pressured.And if you find yourself leasing a new car every three years, just be honest that its for you and not your clients.