For example: axe in slot one; sword in slot two; hammer in three. Select slot one and your pre-made axe skill bar is also selected.
That's obviously the most basic of uses. You could have a different build for each weapon slot.
Too tired to expand on this for the moment - just a minor flash of inspiration.
...and I would put major money on this having been suggested before!
Skillbar presets tied to weapon slots
Snograt
PieXags
Well, this is a very minor change of an idea that's been suggested many times before, but still the idea of saving/switching between builds with the push of a button has been suggested before several times. You'll find the thread we're using for this suggestion in the Index thread, adding this minor variation in that thread is the better route.