Wrong calculation. This is the calculation for the upper limit of 16A plug/wire system. For needing 16A, one need not and must not cross its upper limit. For needing 16A, one or more of these conditions suffice, at least for laymen :
1. The lower power bracket than 16 A (say 6A ) is breached, or uncomfortably close to doing so. Just 2 monitors, a powerful PC, a light, a few mobile and laptop chargers are enough to challenge the 6A system.
2. For laymen, just the fact that PSU, e.g. even CX650 from Corsair comes with the bigger connector for which they start thinking of plugging into 16 A.