It could be both Les - it depends upon the piece and the difficulty....some are so complex it is bar by bar.

As a saxaphone friend notes:
Miss practice one day you know....
Miss practice two day's your teacher knows...
Miss practice three days and the whole world knows...

ANY non-musician will notice a mistake. A simple piece played flawlessly is better than a complex composition with occasional errors.

Sincerely,
Gargoyle