IME that total is always the sum of length/width/height..

So to carry something 120" long it would have to be a pole of some sort..

.. and I believe restriction on "single dimensions" (eg length) can apply as well... most often when smaller aircraft are involved, although I suspect 10' might be over any maximum anyway...

My usual airline (NZ) for example has a maximum length for any checked item of 2.5 metres... (8' 2.5")... which is reduced to 1.8 metres for their regional aircraft...