<i>> The user session is kept in a browser cookie, and you have to live with it. This means that the session space is limited in size and type: you can only store strings. If you need to store objects, you’ll have to use the caching mechanism we discussed before. </i><p>This isn't quite right, or at least is presented weirdly. Caching is not done on a per-user basis whereas sessions are tied to a user. Scala chooses to use client-side sessions so that applications are automatically non-sticky which allows for effortless failover and horizontal scalability.<p>The caching mechanism will cache the output of a template but it's going to be cached for all users. Again, it makes for easy horizontal scalability, but you'd never say that the caching is an alternative to session data. They're for two totally different use cases.