I learned it the hard way. Had an excel template which analised results from a test. It runs for 30-60 minutes depending on the amount of data. If you have another file open in excel and hope to work on it, forget it. Tried it, all data in the other spreadsheet was corrupted (results written in the wrong sheets due to other window being active). The only wise thing was to wait. This was helped by the fact that excel was using one core fully and the other 3 were thermal throtled so the laptop was unusable.
In 2 separate companies I wrote java software that loaded .xlsx files with thousands of rows of rules written in 2 different proprietary ill-specified languages that were then interpreted by the java program.
I once worked on an early era "smart" phone whose apps were written in a visual basic-like clone. We were silicon valley cool kids and thought people would love too write apps in a high level language rather than C or C++. This was pre-web, pre-javascript, pre-Android, pre-iOS. The large Japanese tech company putting the phone out was staffed by a bunch of electrical engineers whose idea of programming was a table driven state machine, so they used Excel to model the UI for the entire phone as one huge state machine, then wrote Excel basic that took that spreadsheet and generated the proprietary basic code for the device's UI. We thought they'd want to write basic code, but they wanted to code up a spreadsheet instead.