Well, the simple answer is if whatever supplies a good spark at the right time does what its supposed to do, then you ride away. A good maggie does the job with no worries about batteries etc. I remember seeing a fire pump, some 50 years ago, powered by a Ford Sit Up and Beg E93A Sidevalve engine, with a magneto in place of the usual distributor. Aircraft ignition was by magneto, so in the right place with service back up and regular maintenance they do the job, and in places where failure could be life or death. I suspect many magneto problems are down to poor maintenance, poor quality pattern parts and the obvious condenser ageing and ultimate failure. But a good magneto is certainly up to the job.
The move to cheaper battery and coil contact breaker systems on later bikes meant a good spark at starting revs, and possible better protection from rain and damp, but the downside is the ability to maintain a well charged battery. How many had bikes that ran for years with the switch set to "Emergency?"
For our models, add up the cost of a full magneto refurbish, and like RoyC, electronic systems become increasingly attractive.
Swarfy.