The point is that it's for emphasis of a part of a song. And it all has to do with the style that you're playing. You're probably not going to hear a Tele going through a Twin in a death metal song. It's the same thing on a different instrument. There's no point in arguing because this is MUSIC we're talking about, an art form. There are no rules. We, as musicians, play what we feel sounds best, and that is all that matters.
Even though I'm not a drummer, and 18" crash sounds a lot different than an open high hat. As long as you're not slamming away at the thing at full velocity, then it can sound quite nice, given the appropriate place in a song.
Which brings me to my next point: velocity. VMattyV, if you're going for a more realistic sound, then I'd suggest trying to think like a drummer. A drummer only has two hands (one in the case of def leppard, but that's a different story). Thus, only two drums can be hit at a single time with the sticks, and then two with the pedals. In addition to this, every drum is not hit with EXACTLY the same force. Drummers will usually accent the downbeats, especially the first and third (except in reggae/ska). Another thing to consider is how heavy handed a person is. If a drummer is right handed, you'll hear a lsight emphasis on the right hand as opposed to the left. The ideal drummer is ambidextrous, but since we're all human, such precision is impossible. I always throw in a couple hits that are relatively louder or softer than usual as a "mistake" for a more realistic sound.
Again, I'm not a drummer, so take my advice with a grain of salt.
One last thing. If you can afford it, try to get better samples. If not, then at least try to fool around with a nice free kit like
ns_kit7 free as it will be a lot better than the samples included with FLstudio.