The benefit lies in the fact you're sharing those channels with N other users. If you have, say, 4 x 55Mbit channels giving 220, three 100M users running flat out will max it out and get about 70% of their maximum speed; bond 8 channels instead, four could be running flat out and still have headroom for a bit more activity without anyone hitting contention.
There's also a benefit in latency: a 1 megabyte burst of traffic will clear in 18 milliseconds instead of 36, for example.
When managing a cable network like this, when a segment is getting too busy at present you 'segment' it: chop it in half, and give each half its own set of channels for connectivity. A single segment with 8 bonded channels will give everyone a better service than two segments each with 4, because the load is evenly divided in the first case, instead of a static division of users between the two blocks of 4.
