The Transcendent's cultivation must first ensure sufficient "stability"; the spirit and body must remain synchronized, coordinated.
Borrowing power that does not belong to you to prematurely comprehend the scenes of the next step is likely to lead to a situation.
That is... loss of control!
This is why Lian Zhou chose to wield the "Paper Scissors" to cut through his enemies; he had to appear strong enough, and sufficiently ruthless, to make his opponent concede directly... Overusing borrowed seven-layer strength and the third-tier domain in the real finals could lead to situations of "loss of control."
Even the slightest hint of it could easily be noticed by others!