Where I grew up, exams disallowed any calculators or any kind of other electronic devices. From what I see, using calculators at exams is mostly an American thing.
For a trig exam for example if you don't allow calculators you are very limited in terms of what you can do. You could do a lot of trig identities etc but all the problems with a concrete answer would have to boil down to some sort of 30/60/90 or 45/45/90 right triangle. It's not reasonable to expect people to be able to calculate exponents and logarithms in their heads either beyond very simple integer bases and small powers. Forget about natural logs for instance. Likewise anything which depends on trig, exponents, logs etc eg converting rectangular complex coordinates to polar, adding vectors fitting any kind of exponential model, etc.
For a stats exam calculating things like standard deviation etc are almost unbearably tedious with a calculator let alone without, but you do need to be able to demonstrate you can do it.
Exams problems are designed to make use of only basic scientific calculator features, I doubt you have the need, or the time, to start sneakily writing VB scripts to try to gain an edge, while the proctors are not looking.
Feel free to adapt it to modern days but the concept stays the same.
If you don't include WiFi hardware, and don't plug in an Ethernet cable, cheating would be extremely difficult to say the least.
What sort of "defeat" are you taking about?
In the Netherlands we also had to have calculators during exams, because some questions just need a calculator to be solved. Especially for stuff like calculus plotting graphs is really useful.
I didn’t need a very advanced scientific calculator, in the exam it was mostly used as a replacement for log tables (remember those?).