It is matter of personal taste. Some clean everything. Others clean only BJ or Chipco type chips that do not have hot stamps since cleaning them can remove the HS. Some go so far as to use polishing compound on crest and seal chips to remove cigarette burns. Some don't clean any chips no matter how dirty. Cleaning seems to help the appearance of most chips except very worn chips where the dirt actually brings out the details that get lost once cleaned. In a word it is just a personal decision. I personally like reasonably clean chips.