Tabs are not used for aligning! They are used for indenting! If you want to align two variables up, use tabs to get to the right indentation level and then use spaces.
File size? Who cares.
The main benefit of tabs over spaces in my view is when you're in an editor that doesn't group spaces into a "tab" (i.e. if you press delete to reduce indentation, it deletes 4 spaces not just the one), then it can be a bit awkward in some cases to reduce indentation. You may find yourself putting one space too many or one too few.
File size? Who cares.
The main benefit of tabs over spaces in my view is when you're in an editor that doesn't group spaces into a "tab" (i.e. if you press delete to reduce indentation, it deletes 4 spaces not just the one), then it can be a bit awkward in some cases to reduce indentation. You may find yourself putting one space too many or one too few.