There has been a lot of confusion, even to this day, about fitted mesh - and my fitted mesh in particular - so I'm going to try to explain to the best of my ability what fitted mesh is and how it works for the residents in Second Life who aren't interested in the mechanics or makings of creating the mesh, but rather in just what it IS and what it means for them, without all of the technical jargon. This is to just help you understand how to use fitted mesh.
Fitted Mesh Explanation
Linden Labs definition of Fitted Mesh:
"Fitted Mesh is a technique in which an avatar's collision bones are used to add further deformation detail to an avatar or clothing. The benefit of this technique is that it allows Mesh clothing and avatars to be adjusted using an avatar's Body Shape sliders in the Appearance Editor."
To explain this more simply, Fitted Mesh is mesh clothing that will adapt to the shape of your avatar and it will change with the Shape slider scales on your Edit Appearance tab. There is no need to have 5 standard sizes anymore because the one fitted mesh item will change with the shape of your avatar. It's very much like a One Size Fits All mesh.
Watch this video to see how Fitted Mesh works:
Why can't I see the Fitted Mesh properly? It's all crazy looking!
This could be because of 3 reasons. First, do you have a Fitted Mesh enabled viewer? You must have the latest viewers in order to see fitted mesh properly. If you do but are still having problems seeing fitted mesh right, this is most of the time fixed by doing a HARD CLEAN UNINSTALL of the viewer and then reinstalling the viewer. If you still encounter a problem then you may have run into a known SL server side bug that is affecting a small amount of SL residents that makes Fitted Mesh look defected. This bug has nothing to do with the fitted mesh creator, and there is nothing the fitted mesh creator can do to fix this.
Why do I still need to use an alpha layer if Fitted Mesh is supposed to conform to my shape?
Fitted Mesh is still made to fit around the default Second Life avatar, which is very outdated and has many jagged edges and rough sides. Alpha layers are still needed for fitted mesh just as any other rigged mesh because the shape of the mesh is a more natural shape than the default SL avatar. All of those jagged and rough edges are still going to poke through, plus the more natural shape of the mesh will be much better made than the out dated SL avatar. Alphas mask these ugly areas and make your avatar look amazing! Even still, because of the limitations in SL, you may need to tweak your shape a bit just like with the 5 standard size mesh items, just not as much.
Why is there only 1 or 2 sizes of fitted mesh? Where are the other 3 sizes?
Fitted Mesh is made to adjust to whatever size your avatar is. It's a One Size Fits All type of mesh. I generally make 2 sizes (S and L - which means Small and Large) because even fitted mesh has limitations. The L helps fit to even larger avatars. It's my attempt to help fit most ALL avatars, even the very large. The creators who are making 5 sizes of fitted mesh are making it incorrectly. They are rigging the mesh to a custom shape instead of the default SL shape so the deformations of the mesh will be inaccurate. In other words it's trying to fit a shape that doesn't truly exist in the fitted mesh's "mind." So the creator is making 5 sizes to try and compensate for it. True fitted mesh only needs 1 size, with a possible second size for the very large.
Why is the price for Fitted Mesh the same as Standard Size mesh if there is only 1 or 2 sizes?
To put it very simply, creating fitted mesh is a major pain in the butt. If anything, Fitted Mesh should probably cost more because if it is done properly and with extreme attention to deforming detail it takes almost 3 times as long to make. If a creator charged by how long something took to make you would most likely pay 3 times as much for fitted mesh over the 5 standard sizes mesh. All of the deformations of fitted mesh is difficult to work with. So many things can go wrong and require even more time to tweak and fix. Frankly, creators of properly made fitted mesh are giving you a luxury item for the same price of a subpar basic item. It's like buying a Mercedes car for the price of a Ford car.
As more questions come up I'll add to this post and answer the questions to the best of my ability. I hope that this post has helped people understand how to use Fitted Mesh better. One thing is for sure, creators are not out to make life difficult for people. We are truly trying to make things nicer, easier, and better for customers. We're here to make your Second Life better and most will bend over backwards to give you the best we can. So go hug a creator today! You never know the things they have had to deal with today. :)