Ok, the calculating of volume is a very good argument for metric. I didn't think of that one. Thanks for pointing that out. But then again, going from feet to square feet and then to cubic feet doesn't seem to hard to me.
It's not, it's going from there to gallons which is the problem. The units I've seen in use include floz, cups, pints, quarts, gallons, cubic inches, cubic feet, cubic yards and acre-feet. That's two completely different systems with many different bases.
When calculating weight it may help some, but that is only if you are using water. Any other matter and you will need a factor for the density in there anyway. At that point it is just as much of a calculation using either measurement system.
Well, only if the density is in the right units, given there are so many choices. There's also a rather pleasent piece of serendipity that water is about 1 kg/litre, heavy stuff (iron, lead) is roughly 10x that, and air is about 1/1000 of that.
I'm not going to claim imperial is impossible to use: as I said, the industrial revoloution was built with imperial units.
The other examples don't seem to be relevant to me. If I was hooking up a heater, it would tell me how many amps it draws. I don't need any BTU factors or whatever. Perhaps I don't fully understand this example, but thing I have worked with have told me the amperage needed and it is simple to add them up to figure out the rating of the circuit.
You have a garage workshop on a 30A circuit. You need to run say 2 HP of motors at most, 300W of lighting. How many BTU/hr of heating can you fit on that to keep it warm in winter?
To answer that sort of question in imperial you have no less than 3 different units of measurement for power one of which is in fact metric! Of course you can do it. You can go to your machine tools and look up the current draw on the label. Then you can go to the heaters you're thinking of installing and look on the lavel for the current and check it all adds up (don't forget the lights!). Or if they were all in Watts, you just add up, divide by 230 (or 110 depending on the region) and you have the answer.
Or other things. You have a server room. You know how much power the computers take (seems to be measured in Watts). How many BTU/hr air conditioning do you need? And whay size circuit is that going to be on? Again more than possible in imperial but a darn sight easier in metric.
Sure you can always look it up and work out the current, but with metric, you don't need to bother, and that's why it's easier. That's the kind of conversions I'm talking about. You can keep coming up with ways to calculate it in imperial, and you'd be correct, but the metric one is always much easier.
Another might be working how much force some air pressure might exert. OK for working it out in lbf if it's in lbf/in^2, but if it's atmospheric based and you have the pressure in mm/Hg, then that's another conversion (and woe betide you if you want poundals instead of lbf because you're trying to accelerate something).
Miles or used for long distances and fractions of a mile are as accurate as you need when you are using them in daily life.
People use both. That's about a hundred yards away down the road. Or 200 or 400. At some point they switch to using 1/4 mile, 1/2 mile, mile etc. Generally there's not much need to convert, but the use does overlap.
Imperial works, but it was not designed. It grew up and is a vast mishmash of different measurements for the same things, with large numbers of different conversion factors. Ignoring even the fractional things like inch/foot/yard etc (and is it 16ths of an inch or thous?), imperial has two entirely independent bases of measuring volume, one based on cubic lengths, the other based on weights of water.
There are two bases for measuring pressure: based on weight-force per unit area and mm of fluid in a tube.
For power you have BTU/hr (heat), HP (rotational power), Watts (!) for lighting and so on because none of the imperial units seem to fit well.
For energy, there's BTU/calories/kilo (lol) calories, HP-hour foot-pound-force (commonly abbreviated as foot-pound) and probably a few others.
If you ever do anything that crosses those boundaries you have to look up figures in a conversion table. With metric, you never do.