Its doubling and quadrupling (even 10x) the number of housing units that is really needed and that affects everything - more cars, more schoolkids, more water, more trash, more crowds.
This right here is the root problem. If you increase housing density in America, everyone expects a place to put their car, and to be able to use a car to get around, so you don't improve stuff that much. We need to get rid of cars altogether as a primary people-mover; then you can really build things closer together, and not have to waste so much space on parking lots.
Trash and water aren't problems; they don't take up a lot of space, though you do need a source of freshwater to supply the city, but unless you're in the desert that shouldn't be that big a problem. Schoolkids aren't a big problem in urban areas: people aren't having kids any more.
Dense housing is the start of making it more inconvenient. Then, once owning a car is less convenient than other modes of transit, will we see alternatives that are better for those areas.
If you're 10x the number of housing units, there will be less cars though.