Beekeepers want to keep swarming to a minimum for a few reasons.
Swarming can weaken the hive since it means the loss of approximately half of the worker bees and possibly a good queen
Swarms are frightening to many people
Often, the swarm will find a home in a neighborhood tree, shed, wall, or someplace else where they are unwanted – becoming a nuisance rather than an asset to the human community