If the stump is too close to a building, foundation, or other sensitive hard scape that could be damage.

If the are hidden utilities, irrigation lines, or other buried objects that could be hit and are to expensive to be removed or replaced. (The ticket to locate your utilities can be placed prior to your free estimate if requested.)

Hard to reach areas where our equipment cannot t. (If unsure we can measure to during the estimate to make sure)
A tree stump that has expensive plants and trees surrounding it can be ground however, the root system of the surround plants may be damaged.