Sometimes, you know the line you want to edit in a file, and you just need to open the file and get to that line. For example, you just had done a grep -n, and found the line you want, say line 99 of a file.
Sure, you can vi the file, and then type 99G (capital G, that is), to get there.
A much faster way is enter this in the command prompt:
$ vi +99 some-file
The above opens some-file and go immediately to line 99.