It is rather difficult to remember the case of each and every filename. And while trying to look for it, or open it from vi, you must remember the filename if you are relying on TAB completion. There is a way to ignore the case for tab completion as I could find from the bash manual.
Add the following line in /etc/inputrc:
set completion-ignore-case on
Now as long as you remember the name of the file TAB completion will always work!