I disagree with the notion that they're only good for absolute beginners. If you can't afford to deposit enough to withstand the high end of microstakes they're great practice for pennies and dimes. On top of that they're not vastly different from $1 buy in MTTs and sngs.
If you're patient enough to see them as more than all in luckfests from hell, there are a great many opportunities for improving your game.
At a glance your basic everyday freeroll is nothing more than an all-in shovefest full of fish. Look more closely and you really can play even better than you imagined for free.
I taught myself some stuff that's considered advanced, and learned it in freerolls.
They're pretty easy to break down. The first level or two you're almost guaranteed to find yourself in an all-in shove-fest of the lowest order. 10's or better say "F*ck It" and call or reraise all-in pre-flop. Just great odds but with a decent hand? Say "F*ck It" and get the chips in.
That's just the first couple of levels though. Later on and with a good sized stack, well...
I taught myself to float, and taught myself when to really get in the thick of things with 2 opponents(there's a trick to it involving stack sizes and putting opponents on hands but still). I manage to C-bet
bluff from time to time. Also I naturally pick up on patterns and the timing
tells of some players. Combine those and I will on occasion call you down with J high to A high because I know my nothing's better than your nothing, and you can "bite me loser".
There's a bunch of other stuff I learned from freerolls that I just can't get organized in my head outside of a freeroll, but still, valuable stuff.
On top of all that I learned the most valuable lesson there is for tournament poker. How to spot the fish and beat them. I'm not after my perceived equals or betters until I'm in really deep. I'm just trying to take chips off of inferior players. I could never have spotted them without the practice.
"If you look around the table, and can't spot the fish - chances are you're the fish" Until you have some practice(and free practice kicks butt) you'll always be the fish.