Bore sighters are rough zeroing tools that help make it easier to get the first shots on paper when actually zeroing. It is NOT a precison instument, in no sense of the word. That's why many people dispense with them and just go sight in at the range.
That said, an optical type bore sighter, one with a grid, does have a good use for hunters. Once the scope is adjusted to point of impact, stick the bore sighter on and carefully note where the cross wires show on the grid. Then, prior to going on a hunt, recheck to see if the cross wires are still at that point. If they are, you can go hunting with more confidence. I have an old Bushnell "Pro" boresighter and keep a card with the zero points of all my rifles in the case with the tool. This pretty much eliminates any lazer bore sight tool, for me anyway.