Well yes and no. What would happen if I have 2 rolls of 50m and want to produce 100m cable? I guess Odoo would try to "combine" these 2 rolls as it would seem together they provide enough. That would be OK if we were talking about pieces, kilos, litres, etc. - i.e. any units that are "joinable". But this is a different case.

Ahhh, I did not think of that....interesting problem.
You could treat the shorter offcuts as separate products.
E.g. Cutting a 100m cable into a 75m piece and a 25m piece with the intention to sell the 75m piece.
In that scenario you could consume 100m in the components on the BoM and have the 25m piece as a byproduct as a separate product.
Consume: 100m raw cable (A), Output: 75m ethernet (B) + 25m OFFCUT (C)
The offcut could then be handled differently in your inventory

In your example, 2 rolls of 50m would be separate products. So your inventory would show that you have 0m of raw cable required to make a 100m roll.

The Offcuts could be used as alternate BoMs for any length shorter than the offcut.
E.g. Preferred BoM for 25m Ethernet = 25m of raw cable
Alternate BoM for 25m Ethernet = 50m OFFCUT (with a 25m OFFCUT byproduct)
and so on...