People don't know you write great code. They don't know you solve hard problems that others can't. If you want to be junior your whole life, then visibility is not important. But if you have ever asked why did he get a bigger pay raise or why did she get promoted instead of me, it is largely because they are visible and you are not. No one in any profession can afford to not be positively visible.
Of course the worst is to be negatively visible. If you do not promote your work, the only thing people will ever know about you, outside your own small group, are the things that get known because they are problems. And everyone, no matter how good they are at their technical work, can easily get known for being a problem employee. Some examples are written about below.
They may not know that you didn't cause project ABC to be a failure, but they will remember that they heard you were on it and they haven't heard anything good to mitigate that, so they will assume you are incompetent.
They may not know that your work was good because the users complained it was buggy when it didn't do something that wasn't in the requirements. Often the only thing they know about your work is what other people have said, whether it is true or not, if you refuse to be visible.
They may not know your work, but they know that you are the one who causes problems because he doesn't fill in his time-sheet and customers can't be properly billed and PMs can't tell how much of the project hours have been burned already or if they are going to need an extension of hours. And doing something stupid like not filling in a timesheet can cause them to eat the extra hours because they were spent before the client knew about them. I assure you everyone up to the CEO will often hear about that!
Without visibility of your good work, you are much more likely to be identified as a problem emplyee and problem employees get the worst performance ratings, get the lowest raises, are least likely to get promoted or get a bonus, and they are first to be on a layoff list.