I used Emacs for several years before I discovered "project" (it's built in). If you're navigating dired trees or similar to find files or grep for strings in groups of files, this is like magic:

C-x p f (find any file in the current "project", e.g. git repo)

C-x p v (grep the whole project super fast)

It's embarrassing how long it took me to realize it was there all along. :-)