You're not loaning dollars, I guess you could look at it as loaning out some Voting Power (VP).
The dollars stay in your account.

The answer to your question is YES there are many reasons for this, first and foremost some of the best examples are the Minnow Support projects out there.

Many of them are bots that automatically upvote your posts, for these votes to be worth anything as far as $ value goes they need Steem Power.
This way we give them some Steem Power and everyone gets something back from it.

You are in fact helping the entire community here on Steemit, even yourself...

If you look at it exclusively from a financial point of view, then there is even more reason to do so, I guess, because in the long run it pays off big time.... most of us have a vote that is worth only a few cents, this way we get votes from some of these services that are way more than we could accumulate by self voting!

So not only are you getting rewarded for your support, in the long run you are actually making a profit so to say, along with everyone else who is pitching in.

Some of the services out there like for example, the first ones that come to mind are @centrelink , @stsl and @mrsquiggle help out groups of people without any prerequirement to delegate, so it is all about a team effort and making things on Steemit even better than they are now.