36 spoke wheels have the advantage of riding better with a broken spoke. Means using spokes until they break is more feasible. (They probably also go longer before they do break.) So money AND labor saving. I rebuild my wheels with the same spokes and new rims, usually twice. I may shed a spoke or two that last build. (Rebuilds of identical rims taped together and the spokes simply swapped over are fast, easier and all the spoke seats are per-bedded.)

Now, I find trying to build wheels with more or less spokes than the rims and hubs are drilled for is living life the hard way, so in practice, I stick to what's readily available. For better, lighter road rims and hubs, that's usually 32 hole. I do seek out 36 hole for my lesser/heavier wheels for my city bikes (in part so I can keep riding the Campy Tipo hubs I am rather fond of).