From Tapestries MUCK
Handling BDSM scenes online is a bit different than it is in RL. The physical barrier between the dominant and submissive creates some problems, but in some cases provides some useful tools as well.
Do not underestimate the emotional impact that scening online can have. Done well, it can sometimes become as in depth emotionally as a scene in Real Life (RL). This can make for a lot of fun, but it has some downsides too. Aftercare is harder if you can't be physically present, for example.
In real life you get a lot more clues about the state of your partner than what you get online. Body language and the tone of a person's voice are just two of the things you lose communicating entirely through text. Some people are better at expressing their emotional state through text than others.
One problem this can cause is misunderstanding your partner's state. If you think something is out of place, ask. Be careful not to guess what they mean, get a clear statement from them.
One up side is that out of scene (or Out Of Character (OOC)) communication in an online scene is a lot less disruptive to the headspace. You can commonly use whispers or the ooc command to ask questions or give feedback about how the scene is going with out seriously impacting the feelings involved. Good communication this way can avoid a lot of trouble later on.
The lack of any real physical interaction limits a number of things that you can do. For example you can't give a sub a real endorphin rush through a beating. On the other hand, this frees you to experiment with forms of play that would be utterly unsafe RL, or simply impossible. Be it through play that would cause real damage to a person, or using imaginary high-tech toys or magic.