On Friday President Obama rolled out a planto pay for two years of tuition at community college, which could affect some 9 million students if all states participate (and if Congress funds the program). Higher education experts are hailing the plan as a potentially high-impact way to help more people enter the middle class.

“Universal high school unleashed decades of innovation and talent that fueled growth, both in manufacturing but also in knowledge sectors,” says Josh Wyner, director of the College Excellence program at the Aspen Institute. ”So the notion that we’re extending universal education to the first two years of college is really kind of a moonshot idea. We know high school isn’t enough anymore.”

So what good is two years of free college, anyway? Well, it depends on how you use it — and whether colleges are able to provide the support that students need to make the most of it. Here are some things to keep in mind.

Chelsey Gillum glances at the crowd filling the Carson Center during the West Kentucky Community and Technical College commencement ceremony Dec. 15 in Paducah, Ky.  (AP Photo/the Paducah Sun, John Paul Henry)

1) Two-year degrees help you earn more.

There’s lots of evidence to show that associate’s degrees, which typically take two years to earn, boost a student’s wages over what he or she would have made with just a high school education. A 2011 review of the literature found that each additional year of school raises earnings between five percent and 10 percent per year. The results are especially good for women: A 2012 study of community college graduates in Kentucky showed that women with associate’s degrees made an extra $2,000 per quarter in the early 2000s, while men made an additional $1,500. Then there are various certificate programs, which don’t show as dramatic results but tend to at least be worth the cost of attendance. It’s not as much as the gains from a four-year college degree, but it’s also not as expensive.

2) Some two-year degrees make you earn more than others.

An associate’s degree in English literature probably won’t get you very far. A degree in a fast-growing health-care or information technology specialty, by contrast, could earn you a lot: Radiation therapists and dental hygienists, the two top-earning two-year degrees ranked by EMSI, make $38 and $35 an hour, respectively. According to another EMSI analysis, the biggest gaps for projected demand and supply in middle-skilled fields are in marketing, sales, hospitality and tourism fields. The moral of the story: Even if tuition is free, if you’re going to spend two years of your life going to school, think about what might get you a well-paying job on the other end.

3) Two free years could help more people actually graduate.

Lots of people enter public community colleges every year. Only about 20 percent finish with a certificate or degree — and getting a degree is much more useful than leaving with just a few credits. One reason is that a lot of people have to work while going to school, and according to the Aspen Institute’s Wyner, working full time diminishes your chances of completion considerably. “So if you can use the money the free tuition frees up to work fewer hours, that makes a huge difference for whatever program you’re entering,” he says. Perhaps for that reason, the Tennessee program on which the White House’s proposal is based requires students to go full time.

4) Two free years could help you afford the next two, three or four years.

If Obama’s plan were enacted, it wouldn’t be the only source of college aid for people who can’t afford it. There are also Pell Grants — but eligibility for Pell Grants only lasts for six years, and if you’re doing a four-year degree working half time, you’re not going to make it. So if you can use the free community college tuition to rack up some credits, that makes it a lot easier to finish a bachelor’s degree before that federal aid runs out.

5) Community colleges could use the help.

During the recession, there was a big run-up in enrollment at community colleges, as people who lost jobs went back to school for retraining. That surge has receded. Enrollment dropped six percent just over the past year, even as colleges launch new online programs to reach more students where they are. So there’s slack in the system, making it easier to accommodate millions more students with the wherewithal to attend.

6) The program won’t pay for everything.

There are lots of questions still to be answered about how the program will be funded. In particular, it’s important to know that the president only proposes to pay the full tuition for two years of community college, not the full cost — the sticker price represents less than half of what’s actually needed to supply that education. Also, higher-value degrees are much more expensive than the average tuition that the White House wants to contribute.

Finally, in some places where community college tuition is already fairly low — like California — all the other expenses associated with school are actually a student’s most limiting factor. “The cost of going to college is not just the tuition,” says Tom Bailey, director of the Community College Research Center at Columbia University’s Teachers College. “It’s also if you have to give up your job or reduce your hours or pay for day care.” The White House’s fact sheet does include language about requiring participating institutions to adopt reforms proven to improve student outcomes, including helping students pay for all those ancillary costs.