Do you actually need to convert units a lot in your daily life? Or compare things to the freezing/boiling point of water?

For me, the major advantage of the imperial units is that they're all approximately human-scale. My foot is about a foot, my stride is about a yard, and it's surprising if I encounter weather outside 0-100F. A pint is a big drink; a cup is small one.

I'm a scientist, and all this goes out the window in the lab, of course. Even there though, a lot of the useful conversions do need some arbitrary constant (e.g. density, molarity) and the SI prefixes are not incredibly useful. I've literally never heard anyone measure something in deci/decameters. In practice, we tend to pick a unit that's approximately the right size and and stick with it--tiny things might be between 0.05µm and 2,500 µm, for example.