To better evaluate how much bandwidth to reserve to each queues, the router needs to know your maximum upload and download speeds. It also allows to reserve some buffer to prevent latency increases from bufferbloat occuring when you fully saturate your ISP link, by setting max rates about 5-10% below the max link rate your ISP is providing.
You most likely don't need QoS for 1 Gbps speed at home, because the remote servers you connect to will very rarely be able to saturate such a fast connection, leaving plenty of bandwidth for other simultaneous connections. I disabled Adaptive QoS after upgrading to 1 Gbps FTTH here.
It might only make sense in a business environment where you may have 20 employees with 20 VoIP phones.
You need to use Adaptive QoS at those speeds, because the CPU cannot handle 1 Gbps of NAT trafic without NAT acceleration. Traditional QoS disables NAT acceleration so it can get full control over the trafic. Adaptive QoS does not because it's implemented as a kernel module, and interfaces with Broadcom's API.