I used to use local set-ups, but abandoned this because live hosting on a proper internet server is way better for proper testing.
I have a dedicated hosting account where I have about 50 to 60 zencart installations running - each one configured for specific environments and testing situations.
20 years a Zencart User
I think we're talking about the difference between someone working on their own site and someone doing it professionally, with the resources and the need for multiple server installations.
The point about database changes and live shops is valid. There has been discussion and directions in the forum about merging customer/order tables when moving an upgraded cart to the live location. I think the usual advice is (when ready to move) put the live shop down for maintenance, copy its db into the test shop, redo any db changes, make sure it still works right, then move it to the live location and reopen. A more direct method for those who are knowledgeable may be to move just some tables from the test db to the live db - only for the bold and competent!
Bear in mind that the minute you create a backup (or copy) of your database, it is nothing more than a "snap-shot" of its contents at that point in time.
That is why it is important when doing upgrades, or reconfigurations to the database, to put the store "offline" (maintenance mode) so that activity that influences changes to database content is stopped.