Calf hair is a great suggestion, and I think tying Wullf's is the best way to learn the basics of winging. It is an art, but anyone can become a wing artist with a bit of practice. Yeah you can leave them off or tie a parachute and catch fish, but then again you can buy a spinner and catch fish. A tyer should be able to tie wings upright and divided from flank feathers, hackle tips, quills (I still struggle with those) and hair.
There are two practical reasons to include wings. First, they are the first detail that a fish could see as the fly floats into the fish's vision window. Many believe that this represents an important trigger. Personally, I don't think it matters for this point if the wings are divided, and on smaller flies I agree you can do without the wings because the hackle will to some extent provide a wing-like profile. If I'm using a light dun or ginger hackle, I will try to use a darker shade or a barred/grizzly version on the smaller sizes to add a bit more substance to the hackle to compensate for the lack of wing. The second reason to include wings is that they help "****" the fly as it is falling and increase the likelihood of the fly landing correctly. This is historically why the upright divided wing developed. And here you have to look at a balance between the properties of the winging material and the degree of separation. An upright undivided calf tail wing will not likely land properly because it will be top-heavy. Divide the wings and they act as airfoils to **** the fly as it falls. Cut/burnt wings or hen tips add a lot less top weight and the divide can be less or none. So I divide hair wings and flank feather wings (wood duck, teal, etc). I don't divide hackle tips or quills, but I post them so their natural curvature provides some separation.
Of course there are no rights or wrongs and in the end it comes down to personal choice. But keep in mind that you can only choose to not do something that you can actually do. If you never learn to tie wings, you can not choose to leave them off.
Mike.