I have to agree with Burb lover. I've always gone by the credo of use the "right tool for the job". After working as a mechanic of one sort or another for 50+ years I've collected duplicates of a lot of tools so have no problem having the same sizes in multiple places at once. The only cross over size I'm comfortable using is 3/4 and 19mm, I even have some impact sockets that are labeled 3/4-19mm. The only other time I have used meteric on sae or visa/versa is when the proper size doesn't fit because a fastener is a little under size due rust.
I can't tell you how many times over the years I've had to "fix" something someone else has screwed up by using the wrong tool, both customers and coworkers. I have to admit I've wanted to smack some on the back of the head for doing stupid stuff but most of the time was able to turn it into a teaching experience.
Anyway as already mentioned there are a lot of inexpensive wrench and socket sets out there today that admittedly are not bad quality so there is really no need to take the chance of rounding off a fastener using the wrong type.

38 Chevy 1/2 ton being resto-moded
65 AC Cobra replica
USAF vet