It is recommended to use the smallest classes of scans, so rather than scan /14 or /8 (which could be a lot of hosts), scan at the most /24 (class C) and have several of them run at the same time. This provides the following advantages:

  1. Finishes quickly. If you scan /8, it can take hours or even days to complete. While having several /24 will allow you to see the results more quickly, there is no benefit in scanning more hosts. The results are the same if you scan 2, 4 or 10 hosts.
  2. You can run several much smaller scans at the same time window and use this to maximize your scanner's capability. By default, the scanner scans up to 8 hosts in parallel. Combining several scans can give you more per second tested host than one scan. 
  3. The results are easy to combine even when the scans didn’t occur at the same time.
  4. You can control a smaller scan time window more accurately. Most scans of /24 take about 1 hour to complete, while an /8 scans' scan length varies more.