Self made projects are a often a huge benefit when looking for a job, especially if you've shipped it and it's running live somewhere providing value to actual people. Next to that is an open source repository, which offers the chance for the team who might be hiring you to get a glimpse at your coding style, proficiency with the languages used and thought process for how you solve problems.
The other main reason you should start a public developer profile now is because you don't want to be a data point when you go looking for jobs; you want to be a line. (different context, but roughly same idea) Especially for someone coming fresh out of college, it can be difficult to judge how much passion and staying power someone has unless they have a visible record of accomplishments to reflect on. If you start a profile now, and work on adding only 1 item to it every month, by the time you graduate you will have done much more than most fresh graduates... or at least it will look that way, and that will get your foot in a lot more doors than just drafting up a resume after you graduate.
EDIT: in response to your comment
Yes your collegiate projects have value when they are your most recent demonstrable experience, especially if you maintain them after the class. It shows glimpses of your level of interest in what you choose to do and a work ethic most fresh graduates (undergrads anyway) have to convince employers of with their words only.
By adding 1 item per month, I mean read a technical book, critique blog posts which are interesting to you, commit to an open source project*, attend a meet up, publish an app and get people to use it, answer 25 questions on internet forums, get in a technical discussion on a tech news board, and the list goes on. If you do only one of these things per month, within a year you'll have a decent history of public artifacts to share on your Careers profile.
Most places you'll interview at will start by asking you about yourself and the things they already know about you. This is largely to help you calm down by talking about something familiar, but it's also to confirm you are capable of talking about something in depth. By showing them your public artifacts before hand (by highlighting your Careers profile in your cover letter), you are giving them a list of starting points to skip a few levels deep into whichever topic they choose. In this conversation, you will more quickly reach the point of showing them how you discovered non trivial solutions to the problems you have worked on. That's something that is much harder to do without giving them this kind of in depth glimpse at what you know before hand.