A2A
Creating puzzles in any volume requires computer assistance. Creating puzzles completely by hand is just too slow. Fortunately, there is a middle ground between puzzles completely created by computer (almost all Sudoku) and puzzles created completely by humans (a tiny fraction). The puzzles we create in-house at Puzzazz (including many by me) are partly made by a human and partly made by a computer. Check out this answer elsewhere on Quora (which also includes four puzzles of mine):
Roy Leban's answer to What is the process of creating a Sudoku?