A while back, partner's then phone became unusable (battery failing within an hour or two of charging). Obviously needed a new battery or phone.
But, on a temporary basis, I could easily have lent her my phone. (At the time, I had a work phone which would have been sufficient for a few days.)
If my phone had been locked, and she used a different network (she did and does), it would not have been possible.
In other words, entirely innocent and necessary behaviour prevented by locking.
Current information suggests that unlocking can be slow with networks sometimes taking several days to do so. And corner shop unlocking is not exactly a wonderful approach with Covid-19. Again, issues which will be avoided in the future.
We see much criticism of the Three network in the UK, but they have not locked phones for almost seven years.