I use both systems interchangeably, often on the same equipment.
An intelligent example: from the late 60's onwards, Rupert Neve and Co. made the modules that sit in their studio recording consoles 45mm wide.
The consoles channel sections, or 'buckets' that hold the modules, commonly in sets of 8 or 12, were multiples of 1.8" wide.
In the horizontal aluminium extrusions that make up these buckets, lie threaded strips so the modules can be held in with thumbscrews.
The tapped holes in this strip are spaced .2" apart, even on 'later 'metric' consoles, and can therefore hold the 45mm modules 1.8" apart.
The result of this is two-fold: The modules, when in the console, have a gap between them of .7mm, since 1.8" is 45.7mm, and therefore never jam, or are a sloppy fit.
The second benefit is that the console frame metalworker only has to work to two significant figures, everything being multiples of 1.8",
and the module metalworker only needs to work to 45mm.....
A very elegant use of two systems at once.
If I'm making a big piece of gear, I'll join it with M4, M5 M6 bolts etc, but if the work requires a very tight tolerance,
I will cut the aluminium using millimetres, but tap the threads BA. This is FAR better than using metric in aluminium, for many reasons.
A _much_ better thread for soft thin materials - stolen from Swiss watchmakers 100+ years ago.
( BA is actually a 'metric' thread- they all have a relationship to each other, and the clearance size of one is the tapping size of the next, in the even or odd number sequence. The even numbers were used widely, the odd numbers rarely, which is why the GPO made all their equipment use the odd sizes, so employees wouldn't steal the nuts and bolts...! )
If you have a small telescope or camera, the thread in the bottom is 1/4 20tpi BSW (Whitworth), NOT metric,
and the thread ( often in the plastic bottom of a camera) therefore doesn't wear quickly, like it would with metric.
If you are interested in mechanics, both systems should be used.
If you have no interest whatsoever in nuts and bolts or measuring things, the metric makes sense.
The Americans take Imperial a bit too far- if you buy firewood, you have no idea how much a 'Cord' is,
and to sound impressive, they insist of using 'thousand of pounds' when describing the weight of a truck, or the thrust
of a jet engine, when 'tons' would make more sense, and is easier to envisage....
Just my 2¢ (1.5 pence)