Just moving through the void, Musk could already feel it, if his strength is not properly controlled it might cause massive damage.
"I can't let my main body leave the sect from now on. Other than learning to control my strength, it is best to focus on comprehending principles. My body has reached the point where it is at the limit of the world. This clearly means that if I don't suppress it it is massive." He actually already knew this.
The moment he broke though, his body was supposed to be massive and yet he has maintained the original form. It was also suppressing his advantages, of which the speed of Cultivation was included.
With a massive body, the massive energy he could absorb, would be entering the world from every direction.
The only problem with this was that the state of the sect might have been disrupted. Since he didn't want to bring about chaos, he let his body retain the small size.