I would expect that much similiar to Jiraiya and Minato's Sage mode, it would increase the speed, and devastation of their attacks which are already rather destructive.
I think it is not just about a heighten chakra pool but I believe they would achieve perfect healing like Hashirama's Sage mode.
Releasing and storing the power in their forehead could be done easily probably.
Although I always thought since Jiraiya had his frog Senjutsu and Orochimaru had his Snake Senjutsu, and since they are were the legendary Sannin, I assumed that Tsunade's Byakugou was actually her form of sage mode.