Good practice for micro stakes and freerolls
But seriously, it is different. Years ago my son was playing for play money and built up to millions of play chips. He got to thinking "this is easy". I got nervous about him underestimating the risk involved with real money
and overestimating his skill level so I staked him with $200 which he then proceeded to lose in a few days. Lesson #1 complete.
We talked about BRM and learning poker, so he started studying the math and reading up on strategy. I staked him again. He played lower stakes and quadrupled the money in a week, paid me back and continued to play a little. Lesson #2 complete.
He stopped playing when he went to college, just too busy. And now he's lost interest.
That story might be a little off-topic, but it makes my point. Just the fact that there are free reloads in play money makes it a whole different world. And while I'm sure there are some players who try to play as if it is real, there are way too many who just don't care.
Play money is good for learning the mechanics of online poker, ie how to physically bet, how the software works, etc. if you've never played before.