I'm not even going to do an example write up from a game session for this. It would take to long, pages probably, to show just how bad splitting up the party can be. It's much easier to get to the bullet points of the entire subject instead of making you read through all that badly done script writing that I do. Mind you this is something that is bad for both the GM as well as the players. But also bear in mind that sometimes it does work and I will cover that at the end.
Let's start off with why it's bad for you since that is what most players are concerned with... themselves. It will cut your game time down considerably. Let's say you play in a six hour session with four other players and you all split up and go do your own thing. Now instead of being involved in the same stuff at the same time the GM has to bounce from person to person. So you will be going from six hours of game time to about an hour and twelve minutes. All that other time you will likely be setting at the table waiting as the other players get their turn at being the center of attention... one at a time.