Code golfing encourages factoring out coincidental (as opposed to fundamental) redundancy, which is bad for understandability/​maintainability. For example, there are C golf programs that read (coincidentally useful) characters from their own source to avoid having to include string literals. Basically, golfed code tends to have fragile interdependence between parts (high coupling), which makes it hard to extend.
Code golfing encourages factoring out coincidental (as opposed to fundamental) redundancy, which is bad for understandability/​maintainability. For example, there are C golf programs that read (coincidentally useful) characters from their own source to avoid having to include string literals. Basically, golfed code tends to have fragile interdependence between parts (high coupling), which makes it hard to extend.