When you grow up metric (cgs) you quickly develop a feeling for the units in that system. A cm is the width of my nail on the smallest finger, 10 cm is the length of longest finger etc. I can use my body easily for everything I need in my daily life, I even know what 1 degree visual angle is using my body.

Metrification (unification) was a necessity in Germany some 150 years ago. Of course we also had old measures like foot, Elle etc. But in each German statelet these measures were slightly different. That was never a problem for the local users, it was a serious problem for long distance communication, science and trade.

Wolfgang