The way `grep' and `vc-git-grep' works right now is that it will always output its result to a buffer called `*grep*'. So, if I perform another `grep' command, it will overwrite the previous grep result (unless I rename the buffer beforehand).
I would like, at least, an option to create a new buffer each time a `grep' command is executed. Maybe each new buffer could be given the name based on the regexp or the grep shell command used.