Quote from Dewin on January 6, 2008, 4:46 pm

In my experience, moving a selection of objects that includes at least one brush will favor keeping the brush aligned to the grid as opposed to other objects.

This comes in handy if you need to align a bunch of objects very precisely (say, at a grid size of 2 or 4) and then you want to move the whole 'cluster' of objects at a larger grid size (say, 32 or 64). If there's at least one brush, a brush will be aligned to the grid and the point entities will move relative to it.