If you have grass there, just mow it. If it's lousy, weedy grass, who cares?. If you have mukch, keep the mulch. Why put miserable concrete over a big patch of backyard? You'd have to pay to get rid of it, later.

Don’t want to maintain and water the grass regularly for the next few years if we don’t need to. Mulch/sand/gravel seem like more sustainable options. Concrete simply allows us to do more with the space in the meantime but certainly wasteful as well.

Concrete is expensive in my area … how large of an area?