I have been involved in stakes since the first online staking site opened. It has generally been extremely +EV for the player because when you are fully staked, you play without any chance of loss to your own bankroll and it is a freeroll. The only costs to you are Time Value.
Many players, both inexperienced and full time pros, have used stakes to build their bankrolls. Many high stakes playing pros are fully or partially staked full-time.
The only bummer about today's stakes, is the percentage paid to the player has shrunk significantly (you have to play for less). When stakes first started it was routine for a 50/50 split. Then Cake/Makeup was introduced, where players owe losses back to stakers before a profit is taken. Then, in the last year or two, average profit splits shifted to 60/40, then 70/30 and some people even play 80/20 now. Also, in order for many new packages sold by players to be accepted, they must include the players own participation (he has to put his own money in it also).
People play one-off stakes for MTTs, series of MTTs, cash game sets (these are hardest to get), live tournament one-offs or sets, and WSOP
stakes (well, these are the hardest to get).
Staking is much more popular than many people realize