I have never had an issue with it. I had a butt dial once because I forgot to lock the phone before I put it back in my pocket but that's not the fault of the phone. I have mine set to require the fingerprint immediately upon locking rather than after a set amount of time. I think that is where people run into issues. I do not personally find that I open apps by accident. I had that problem with the edge screen on the S7 Edge but I felt that that particular problem was addressed with the S8 models.
Another thing, if you answer a text message and then just put the phone in your pocket, it's going to dial whoever you're texting if you have the "raise to call" feature or whatever it's called enabled. People need to realized that as well.