Welcome to the forum!

As Mom said, it removes the filter from the vacuuming equation, bu8t at a cost - you loose pool water, so if you have fill water issues, it isn't always viable. Also, it's only an option if your filter has a multiport - cartridge filters and 'bump' style DE filters don't have multiports (though there's always a way to 'walk around' the issue

If you need more help/ info on this - just ask

BTW - there are no stupid questions here, except the one unasked! No one is born knowing this stuff and the easiest way to find something out is to ask someone who knows