To update the amount of slots available in servers. If they're all full you can refresh to see if theres a slot free. Or if it says 8 and you want to join with a friend, you can refresh to see if its still 8. There are many reasons to refresh actually
Sometimes my favourites don't show at all (before and after refreshing).
I also think that if the browser wasnt bugged and filters would work better, in combination with the browser being displayed in a more appropriate place (so that people know it exists), community servers might flourish again. A lot of new players just click the play casual/competitive buttons. I miss a lot of old gamemodes. Valve has tried to remake some of them (gungame - armsrace / scoutzknivez - flying scoutzman), but made the most horrible versions of those modes possible (with very shitty maps) and killed the real modes by doing so, because a lot of new players don't understand we have a server browser and it even if they do, it doesnt function well. I have to use gametracker to find pug servers for example. It's impossible to find them with the ingame browser.