In case someone has 300 SP (or any other amount) in an account and ONLY upvoting themselves 10 times a day with 100% then you are right. Then it is better to keep it and do not delegate anywhere, do not upvote anyone just selfvote the hell out of the 300 SP I guess :p
Not something I would do or recommend. But it is always a choice of the SP owner.
Just to clarify. Qurator didn't switch to a monthly paid model. We added the option for members that cannot delegate, but would like to be on higher Tier ;)