I don't think it's necessary to lease SP on steemit. Yes it's an added bonus if you have the steem or SBD to do so but it's not necessary. It's not easy, but I've seen accounts who have grown their steempower from scratch all the way up to the thousands. Leasing sp can be done by anyone, but I usually see it done by people who have communities and want to upvote posts of members of that community with the leased SP.

I rarely see people lease SP just to vote themselves, besides the new hardfork is going to put restrictions on just how much you earn from upvoting yourself so although I don't see anything wrong with leasing sp, I don't think that it's necessary as well.