Hi. Yes, you need these things to hide accessories.
When you transfer weights, the vertices might get different weight values even if they share the same coordinates. There are two ways of preventing it:
1). For example, you changed the length of a sweater only in one area. You can separate that whole area and transfer the weight to it ONLY. Then you would join it back and remove doubles in the place where the separated part connects to the rest of the sweater;
2). Join all parts of the mesh into one, remove all the doubles and transfer the weights. After that, you need to separate them back.
To fix your current issue, you need to join all those extra meshgroups to the sweater, remove doubles, then separate them again.
- switch shading to Solid to see where those extra meshgroups are, in object mode select each with LMB, check the cut number;
- open a notepad and write what part of the mesh has what cut number ( r(ight) up(per) arm - (000)1, r low arm - 7, etc );
- select all meshgroup but the biggest one, join them with Ctrl J;
- switch to edit mode, switch to edge select, select everything with A, Select - select boundary loops, Mesh - Edges - Mark as sharp;
- select the rest of the body and do the same thing;
- select the rest of the body and join it with the joined meshgroup;
- select everything in Edit mode, Tools - Remove doubles, set Merge distance to 0,0001;
- Removing doubles normalized the wights, now you need to split the mesh back using the blue lines as a guide;
- select one face within the area, press Ctrl L, choose Sharp, press P, choose Selection. Rename the new meshgroup to the last digit of the cut number it is meant to have;
- after you've done separating all of them, change their cut numbers. You might also want to
remove unused vertex groups from every meshgroup ( type 0, press I want that ( or whatever it says in English ), download, in Blender go to File - User Preferences - Install from file, choose that file, enable it, Save user setting)
