Also, a leaf doesn't have to handle all the search traffic going on. It's "shielded" from irrelevant requests. So your ultrapeers only sends searches to your leaf for files that might match your shares.

This saves you a fair bit of bandwidth, which means your searches and transfers should go a bit faster.

It's good being a shielded leaf. Ultrapeers get other advantages to help make up for handling most of the traffic.