Delete excess columns and rows

This depends upon how you define "excess" columns and rows. By default a worksheet has about 16000 columns and 1.4 million rows. Most of them aren't usually used but they can't be deleted, either.

Cells are made visible by the gridlines that surround them. You can hide the gridlines (from the View tab) but then you would have to draw borders for the cells that you do use, and the cells will still show as a blank area.

If you don't want any blank area you must use the full screen and fill it with your used cells. In that case it wouldn't matter whether the blank rows and columns have gridlines or not because they aren't visible on your screen.

Excel is all about display. Quite often, what you enter isn't what you get to see, meaning, what you see isn't what's really there. Therefore, forget about deleting the cells you don't like and focus on showing what you want to see, hiding - not deleting - everything else..