structs that might require varying amounts of memory
There is a somewhat common use case where a 0 length or length 1 array is used at the end of a struct so that a variable amount of payload can be carried around by the struct. The technique is hardly ever needed in C++ land, there are better ways to handle the problem.
One interesting use case in C land is to provide data hiding. Use a common header struct the provides high level management information, then a variable sized "tail" that gets cast to the struct type that represents the hidden data. That makes the payload data opaque to client code and avoids making two allocations when creating an instance of the struct. Kinda a poor man's C++ really!
Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond