Why divide an overwintered colony?

There is my nectar flow. Up in a tree. I won't get honey from that colony.

This colony is very strong and will swarm. Leaving the beekeeper with no excess honey for the year.

This time of year many new beekeepers with overwintered colonies are unaware how strong their colonies are and how big they will get in a short period of time.
If you have 8 frames or more of brood in your colony by around mid May dividing it may be the only way to stop it from swarming.
I have a link about dividing colonies at the lower right corner of this page.
If the beekeeper doesn't want more colonies there are people looking for bees right now and will be happy to purchase a divide from them.