As he said, it's usually the amount of self vote. The vests make the same value of vote regardless if you cast the vote or if @randowhale does it.

2 key factors that change that but both mitigate each other:

• His VP gets drained from many votes which would shrink the vote value and thus your profit overall

• Between the amount of votes he does cast, he's more likely to catch blogs prior to rapid inflation which would increase the curation rewards given to you