In order to scan hosts efficiently, Nmap uses groups of hosts that it scans at the same time. Assuming your Internet connection (and computer processing power) is sufficient, it's generally better to increase the host group sizes to finish large scans quickly. For example, if you're scanning 1,000 hosts with a host group size of 250, it will only take four "sweeps" to complete the full scan in parallel.

However, one should carefully weigh what they're looking to achieve by changing the host group sizes. The benefit of scanning many hosts at once is clear, but the downside may not be—if you're scanning a large group, you have to wait for the entire host group to be finished scanning before seeing any results and moving onto another group. If you are trying to see results quickly, a smaller host group would be better for your specific scan.

By default, Nmap tries to take a dynamic middle-ground approach to host group sizes: it dynamically changes the host groups to...