Title says it all. A lot of times when I pick up containers, I like to set them down in neat lines. It's a whole lot harder without a snap. Building them on a snap is great, but if you relocate or use the containers in a cart for gathering/transporting goods, you just can't get them back in the exact same spot.
In addition to grid-snapping for placing lifted objects, I think it would be nice to have the option of adding a defined grid when making roads or plowing fields. Sometimes it's hard to tell just where you're clicking, and leads to messing up. By this, I mean a visible grid, maybe bold black outlines or something.
If I'm missing something, feel free to add. Or shoot down my idea completely, both work. =/