i love your question , i think there are lot of reasons to delegate your token for instance, it night be used to support a particular account in rewarding the community .
when you delegate it doesn't mean you will not get and reward in your account, you will also get some reward, but the proof of stake will give the account upper hand in receiving curation share.
what do i mean by that, if you delegate to a particular account and alot of people delegate also, those whi delegate to the account will receive weekly reward and the reward to me is mostly higher than the amount you will initially receive from your own personal curations.