Ctrl+Shift+Click on any group that you don’t want. Then Ctrl+Shift+Drag on an empty part of the canvas to reverse visibility. Now just Ctrl+Shift+Click on any other groups that you don’t want.
You can also Ctrl+Shift+Drag on the mesh, covering the groups that you do want. Then Ctrl+Shift+Click on any groups (or their parts) that remain which you don’t want.
Either way, it takes no time at all to trim the mesh down to just the groups that you need.
Also, if you will repeatedly be selecting the same sets of groups, there’s a shortcut to make reselecting them really easy (provided that you’ve given the mesh UV’s already). After you’ve selected the groups that you want, Ctrl+Click on the canvas. The visible parts of the mesh will be masked. Now press Tool>Masking>Create Alpha to save the mask as an image in the Alpha palette. Clear the mask and continue working. When you later on need to return to the same selected polygons, simply select the Alpha again and press Tool>Masking>Alp followed by HidePt and Clear. You’ll once again have the original polygons visible. You can even save the Alpha for use in future sessions.