Revolving balances matter more than most people expect, since a card sitting near its limit weighs against a score even if every payment has been made on time, and paying it down before a lender pulls the file can move the number faster than almost anything else.
CMHC sets a minimum credit score of 600 for an insured mortgage, so a borrower near that line has the most to gain from a short, focused push before applying, while a score already well above it will see a smaller practical effect.
A mortgage broker can flag which specific factor on a file is doing the most damage before you spend months guessing. Get your hand-reviewed valuation from Joel Dyck.