If you bet a team at -3 and it closes at -4.5, you've beaten the closing line by 1.5 points. Consistent positive CLV correlates almost perfectly with long-term profit. Hit rate alone is noisy; CLV is signal.
Advanced concepts
Closing line value (CLV)
The difference between the line you bet and the line at game time. The single best measure of long-term skill.
Example
A bettor with +1% CLV will outperform one with -1% CLV over a full season, regardless of short-term results.