The goals of transaction relay include: predicting what transactions will be mined (for example for fee estimation or fee bumping, but it is also the basis for many DoS protection strategies inside of node software); speeding up block propagation for the transactions we expect to be mined. Reduced latency helps prevent large miners from gaining unfair advantages; helping miners learn about fee-paying transactions (so they do not need to rely on out-of-band transaction submission schemes that undermine mining decentralization).