If you are solely playing for fun, then freerolls are obviously going to be fine, since you can win money in them but never lose. So its basically free entertainment, and if you cash, you can then go and spend the money in the casino or sportsbetting section, which most sites have.
If you are more serious about poker, then freerolls are still fine to get some practice, if you are brand new to the game. Or you could do, what I personally did back in the day, which was to begin with play money games. You dont want to do, what I also did though, which is to stick to either play money games or freerolls for to long. Actually the first part of my poker story is very similar to that of Nathan Villiams, which tell his story here.
As Nathan I did not want to "gamble" with
real money, but given that you can play cash games as low as 2NL and SnGs even cheaper, that was in hindsight rather silly. As soon as I took the step and moved to real money games, I was right away a winner at 2NL, so if nothing else I could have played these games for free and enjoyed it quite a bit more than the frankly silly play money games, I spend so much time playing on Zynga Poker.
So sure. If you are just starting to dip your feet in and learning to read boards like for instance understanding, that the river card did not help you, if you have Q4 on QT2-T-4, then by all means play some freerolls or play money games to learn those things. Or learn to fold an overpair, if stacks are deep, and you face a ton of heat.
All freerolls are not created equal though. The CC freerolls all have a reasonable blind structure, and those reserved for platinum members also see a reasonable level of play, which is not to different from microstakes games. But there are also other freerolls out there, like for instance
888 Poker offering freerolls with 1 min blind intervals, and these are not nearly as good for learning, since they are simply to different from a normal MTT with 5-12 min blind intervals.
But even if you stick to the "good" freerolls, you need to get into real money games as soon as possible. The reason is, that if you only play freerolls, you are simply not getting practice fast enough. For instance there is a daily CC freeroll on
pokerstars, but if you only play this, its only 1 game per day. Whereas if you add in some 45 man SnGs, you can play maybe 10 games a day and get practice 10 times as fast.
Playing real money games is also the only way to build a track record, so that you have a reasonable idea, you are a winning player. In theory its completely possible to play freerolls, until you have 750$, and then jump into 15$ SnGs. But by not having played SnGs for lower buyins to get there, you wont know, if you are beating those 15$ SnGs, and most likely you are not. And this is why, you should start playing 1,5$ SnGs, and then 3,5$ SnGs, or whatever the limits are on a certain site, to build up a track record as well as a bankroll.
Finally playing freerolls will not subject you to the feeling of losing, and you will therefore not learn how to manage tilt. If you run bad in freerolls, the balance in the poker account stay unchanged, but this is not, how poker works, when you play with your own money. And since tilt is one of the biggest killers of winrates, this is something, you need to learn to deal with, as Nathan talks about in this video: