It really depends on the circumstance. Generally the code should be correct and work as current requirements dictate. So probably you don't want to keep an ent

It really depends on the circumstance. Generally the code should be correct and work as current requirements dictate. So probably you don't want to keep an entire section of the old code just commented out and sitting there. What I've seen done as a practice is to leave a brief comment referencing specific commit hashes in cases where an important change to business logic is involved. Most of the time this shouldn't be necessary though. In the course of investigating bugs, going through the commit history should provide most of the information needed. Do a "git blame" and read the notes the previous person left in their commit messages.