Hi,
The short answer is using larger channel widths enables the capability of raw throughput but often you sacrifice space/performance so it becomes a trade off, particularly in high density environments.
In 2.4 GHz there are only 3 channels (1, 6, 11) that are non-overlapping in most countries and so channel bonding (the name for the larger widths) is really bad in the 2.4 range. A lot of home routers don't really say what they're doing when you select the highest speed possible from a list, who wouldn't click 450 over 300 when given the choice? The problem there is of course absolutely every single device is using the 2.4 range already and channel bonding just ensures your network will cause performance issues for you and everyone around you.
In the 5 GHz networks channel bonding is more common practice. There are roughly 20-25 channels available depending on country so if you bound only 2 channels (40 MHz) you will still get 10-12 non-overlapping channels. At 80 MHz this cuts down to half and for 160 MHz there just doesn't seem much point unless you have a very low number of devices and no neighbours.
This graphic is quite handy to explain the available channels in 5 GHz. It is common practice to use 40 MHz unless there is super high density of APs/Clients and then 20 MHz is fine too. To be honest wireless for the most part isn't about raw throughput it is about each client getting fair, clean airtime so don't let the speed capabilities trick you. 802.11n / 802.11ac at 20 MHz in 5 GHz is easily enough for most clients to do day-to-day stuff.
