Chapter 257:
Sage Mode is a combat state that amplifies one's power several times over—or even dozens of times, compared to their normal state.
It is widely known that achieving Sage Mode requires an exact ratio of chakra to natural energy: 2:1.
The more precise this ratio is, the more flawless the resulting senjutsu becomes.
In general, regardless of which holy land one practices senjutsu in, the more chakra a person has, the easier and faster their training will be.
For instance, Jiraiya required 20 minutes to prepare to enter Sage Mode. Naruto, on the other hand, needed five minutes. The First Hokage, by contrast, could activate Sage Mode instantly.
This alone demonstrates the advantages of having an abundant chakra pool. Not only does it make learning faster, but it also allows for quicker activation of Sage Mode.
As for whether Orochimaru would end up like the original Yakushi Kabuto, with his body becoming heavily snake-like due to Ryūchi Cave's senjutsu? Orochimaru wasn't concerned.
Yakushi Kabuto's transformation had far more to do with his transplantation of foreign cells than the effects of senjutsu itself.
Turning into a snake through training? That would only happen if one's body was too weak or their mastery of senjutsu was flawed.