For me, it's a few things (some of them also identified in other comments here) * Keeping my finger on tech and its changes * A tech community * Off-the-wall

For me, it's a few things (some of them also identified in other comments here) * Keeping my finger on tech and its changes * A tech community * Off-the-wall things to read * Ideas for side projects - e.g. implementing lisps interpreters All of these have got more valuable now that I'm retired and not surrounded by tech peers