Ron Rosenfeld wrote...
....
Why is Split wasteful?

It does more than necessary. It locates every \ and creates an array,
neither of which are necessary, both of which require execution time
and additional memory usage.

And is there someplace I can read about this issue (wastefulness) in general?

Benchamarking, both for speed and resources use. Web search on
programming and either benchmarking, efficiency or performance.