It is only relevant to particular plotters. Furuno, for example doesn't use chips or other removable media.
I think they have a microSD card but it is practically inaccessible being in a slot on the back of the monitor within the waterproof pod. However, these cards can be copied, so losing one is not a disaster - they just have to have the same ‘license number’ as the master.
For most applications, our iPad is fine (at the risk of reigniting the old arguments on this matter). But there have been times in the past 6 months where we took water over the bow that challenged the helmsman to stay standing and may well have pulled a removable mounted unit off. That is not necessarily the type of sailing that most people do (nor that we would plan for) generally.
Also, in addition to overlaying radar, getting real-time AIS has proven very useful. Not quite sure how to do those two things on our iPad.