This is a very recent view of the 8th green at West Sussex with all unrepaired or badly repaired pitch marks recorded using a range ball. Over 150 balls were needed to illustrate the extent of this problem.
Repairing a pitchmark is part of the etiquette of the game and a necessary courtesy to all who follow you. Repairing a pitchmark properly speeds up natural repair by the grasses.
This is good advice (from Todays Golfer) on how to repair :-
1. Take your tool (or a tee) and insert the prongs into the turf at the far rim of the depression, rather than in the depression itself.
2. Using a gentle, twisting motion, push the edge of the mark towards the centre.
3. Flatten by gently tapping the surface using your foot or the sole of your putter.
A mark repaired within 10 minutes will fully recover within three days. A badly repaired or ignored one will take over a week to heal.
Here is a link to a video demonstrating correct repair of a pitchmark (made by Golf Monthly at West Hill)