No further than you want to go. You don't have to respond to any photo request if it does not work within your schedules/travel plans. I think BG gives them to a wide radius in hopes that someone out there will be near the cemetery and be able to do it.
What I don't know is how you can remove one from your profile if you don't want to do it. I responded to one a year ago, at a cemetery near where I usually shop, and after walking the entire cemetery and not finding the grave, I responded that the grave was not found. i still get that notice anytime I open Photo Request Frame.
Doesn't bother me; just ignore them.