It is generally accepted that between 1 and 5% of normal network traffic comprises broadcast frames. With a switched LAN environment, the whole network behaves like a single broadcast domain. Hence, any broadcast frame transmitted to any switch port will be retransmitted over every other port of every other switch. As the network grows so the broadcast frames become an increasing percentage of traffic. Remember also that every client and server will receive this broadcast and must therefore spend valuable processing time analysing the frame with most of them ultimately discarding it!