Changes were made over the years, and only some products need to be deactivated. I think these are the products bought in the Captain Sim Online Store for MSFS2020. These ones would be the ones where you use the ACE to do so.
As for the rest of the Captain Sim products, you are limited to a certain amount of installations (using the instant Online Activation, which I think is three (3) times) before the product gets locked. However, once the product is locked, you can request that it be unlocked, and it will be unlocked. I have had to do this numerous times over the years. Using the Manual Offline Activation allows you to install/reinstall the product multiple times on the same system (same PC with no changes in hardware/software that would cause the activation code to change when installed/reinstalled) without adding each install/reinstall to the amount of times you have done so (the Manual Offline Activation will only count as one (1) until you do it again), and therefore you don't excede the limit so quickly. This was handy when I used to do a complete reinstall of PC every six (6) months, but I don't do that any more (I'm older and lazier now).