performance - Benefit from using ehcache in a hibernate webapp -

i'm working on webapp used multiple user @ same time (on same objects). i'm using spring , hibernate di , persistence. i'm considering adding ehcache family, learn more , how implement in existing system.

basic questions:

1. how can i, using ehcache, 100% sure users newest version of entity?
2. will ehcache benefit in system entities changed often?
3. if benefit minor (lets 3% performance improvement), worth while it? - there other benefits, aside potential performance gains?

not looking code examples, word of advice , guidance people have tried implement ehcache in existing spring/hibernate application.