If you use of
expandtab options in vary ways and try to test them, these options are opposite in function (at least as I think).
et option will produce the appropriate number of space when we press TAB key and when we press BS the spaces will delete one by one in the other hand when we set
sts and press BS it will delete a tab (not spaces one by one).
sts option in vimrc together isn't a good idea because they will break their effect together.
Now am I thinking right? (If not please let me know how they are differ in function and behaviour.)