With the moveobjects cheat, you aren't constrained by slopes, indoor/outdoor rules, or snap-to-wall placements. This includes planting seeds, buy mode placement, or dropping a tent or firepit from your inventory. The latter two are quite useful when your sim is camping out but there is just not quite enough space for a normal placement.
The terrain paint style grasses cannot be done beyond ground level, but all the various plants you can see in build mode, as well as any gardening-related plants, can be placed where you see fit with that cheat on.
Makes it really useful for smaller lots, because you can have a rooftop garden, or in your case a basement garden, and not have to waste space on the ground level for them.