As @Karsten Iwen already noted, generally "nearly nothing"; for example, no problem even on 10Mbps half duplex Ethernet.
However, bandwidth consumption will increase if you decrease timers (and/or increase number of packet per announcement); although usually that doesn't cause a bandwidth issue either. More of a problem with decreasing timers is the increased CPU loading on the device. If available, later platforms support a "light weight", hardware assisted (or so I believer), function that you might optionally activate to decrease CPU impact using this feature (whose name I'm drawing a blank on, at the moment).
