TIL: Denmark switched to the metric system in 1907, but apparently some Danish carpenters still prefer to measure in inches, and Hultafors still sells folding rules with both systems.
Note however that the Danish inch ("tomme") is 26.1 mm.
I use both systems on the fly. Some things are more naturally or intuitively measured by dividing things in half, in half, etc. Others work better in base-10.