I grew up in Australia with SI units I do a lot of work with Fluid/Thermodynamic calcs. I have a bunch of reference values in my head. I know 1 Atmosphere is ~101.3 kPa, I know speed of sound in dry air is ~330 m/s I know how much energy it takes to raise the temperature of various substances. I know the densities of common materials in my head. All of that helps me sanity check calculations - at a glance I can see things 'this fan is producing too much suction, not possible' or 'There is not enough input energy to see a temperature rise that high' things like that.

I have no idea about any of the non SI units. I couldn't tell you how long a "yard" is or how heavy a "pound" is usually it is fine but occasionally I come across numbers in technical papers or datasheets or similar with stuff in wacky units - PSI, BTU and Fahrenheit are the worst offenders when I have to deal with them it just blue screens my mental models. I see those units so infrequently I have no concept of what a 'reasonable' value expressed in those units looks like. I imagine people who don't work in SI units everyday hit the same difficulties in reverse.

Obviously this is slightly more lax and perhaps error-prone than your standard m/s or m/(s^2), etc., but it's one of the lamentably few things computers can do well!

EDIT: ... and I should elaborate: In some sub-fields of Physics they usually go even further and just re-normalize everything to units of 1, so that e.g. the speed of light is c is 1. At that point it's really just about convenience since sqrt(1) = 1, and 1^x = 1, etc. (Lorentz Transformation.)

For example, if I am looking for a force and I get an answer of 1000 lbs, then dimensional analysis tells me that at least I got a force; but, if my intuition tells me only that the actual force is on the order of magnitude of 1000 N, then I don't know whether my actual answer is way too big, way too small, or about right, unless I know how to convert between Newtons and pounds.

Incidentally, while "units of 1" make correct calculations easy, I think that they are a bad idea precisely because they subvert unit checking; it's hard to know just by looking that 1 + 1 is 1 speed of light + 1 light-year, and hence dimensionally inconsistent.

(Even keeping all SI units can miss some important distinctions; for example, nothing about their SI units (inverse time) allows us to distinguish angular frequency (https://en.wikipedia.org/wiki/Angular_frequency) from temporal frequency (https://en.wikipedia.org/wiki/Frequency), and yet much woe accrues to he or she who does not distinguish radians/time from cycles/time!)

With Fahrenheit perhaps the worst of the worst (scum de la scum?), because at least you have an intuitive idea of the meaning of 0 PSI and 0 BTU.

[0] https://futureboy.us/frinkdocs/

Don't understand what something is? Just look at the unit. It tells you!

     a
    b c

  a = b * c
  c = a / b
  b = a / c