BTTS ignores the result entirely — it settles Yes if each side scores at least once, No if either keeps a clean sheet.
It shines in matches where both teams have a clear path to a goal: evenly matched sides, strong attacks against shaky back lines, or derbies where caution tends to disappear. It's a poor fit when one side both dominates and defends well — a routine 3-0 settles No.
A useful lens: BTTS Yes is really a bet against two events (either clean sheet), so look at each team's clean-sheet rate rather than their goals-per-game alone.