[MapProxy] how is the cache purged?

[André Pirard]

Thank you for a great program !!!
This may sound weird, but I couldn't find any answer to this important 
question.
Is the cache purged automatically and how?
Or should one understand that it is not and that the user supposed to 
run mapproxy-seed periodically. Is the standard configuration suitable 
for that and what is the command to run?
These answers should definitely be found under cache in the documentation.