When you install iTunes, you install Bonjour. When you update iTunes, you reinstall Bonjour.
Bonjour is required for sharing music with others, playing music through AirTunes speakers, and connecting to Apple TV, and using iPhone and iPod touch Remote.
Also, Bonjour or Zeroconf is a supported device discovery protocol for non-Apple devices including network printers.
Software such as Bonjour Browser or iStumbler, both for Mac OS X, or Zeroconf Neighborhood Explorer for Windows, can be used to view all services advertised on the network.
I have no need for these capabilities or products. Bonjour is an additional service (running as mDNSResponder.exe), so it is an additional attack surface, and a memory loss. Bonjour advertises services on UDP port 5353, so it is additional network. In summary, in my situation, Bonjour has no benefits and has costs.
Fortunately, you can uninstall Bonjour. Unfortunately, I have to keep uninstalling Bonjour whenever Apple releases an update to iTunes.