What exactly is "vote_when_vp_reached = true" as opposed to "=false"?

That's the only box I don't quiet get, but I've been using rewarding since the Steem days and it has a hidden gem function: vote on a post after payout; I use this extensively.

To do so, comment on any post past payout:

"$rewarding 77%" or "$rewarding 77% 13min" which "creates a comment with 100% beneficiaries set to the author (of parent post/comment) and upvotes this with the given percentage and delay"
Of course you can input any vote weight % and time delay is optional.

I'll give an example on @holger80's post here.