1's are used almost everywhere in freestyle riding, either themselves or as the basis for bigger spins. I strongly think everyone should do what is most fun to them and not follow a specific regiment, but without having 1's down solidly, it's going to be hard to progress without them.
Learning every jib front and backside is also hugely important in terms of building a foundation for complex stuff.
The best place, IMO to get your 1's on lock are side hits, small roller type features and the moguls. Now, some resorts will have a no air allowed in the mogul field, but this is where I learned my 180's. If you can throw a big, lofty backside 1 and stomp it without worrying about landing in between or on top of the next mogul, you'll dial it in very quickly.
The moguls kick ass because you land a backside 1 blind, look foward then throw a front 1 right off the next hit and you kind of start to get the feeling of a 360. Just make SURE there is no one in front of you and make sure there aren't ski patrol around. You can literally 180 your way down the mogul run and get so much practice in.