It has replaced vim’s “open file” and “switch to buffer” for me. I occasionally use it in the command line, by expanding *. Not that often as in Vim, but very useful. I still need to find a satisfactory way to do “find in files” with vim. I use a custom script to call ag and it’s enough, but a bit clunky at times.
If you're using neovim I suggest checking out telescope.nvim. In addition to searching for files, it comes with a Live Grep mode for searching the current buffer (or all files in a given directory). For find and replace, I use spectre.
I also use telescope, but I never found a way to search for a couple of words that are near each others (like on start and end of a line eg)
Does that work for you? I thought that's what a fuzzy finder is