I delegate out approximately 50% of my HP, primarily to projects that share most or all of the curation rewards to delegators. I do this because I know there will be occasions that I just don't have the time to be on Hive. It's a way for my stake (or at least part of it) to keep earning even on those relatively rare days I can't give it the attention I should.

Having said that, I don't intend to ever delegate more than 50% of my stake and I will probably reduce or remove those delegations at some point.