The marking scheme is the point
Questions without a marking scheme create work rather than saving it. Both are produced together, so a worksheet can be set and marked without writing the answers out afterwards.
Matched to the format
Question style, command words and mark allocation follow the examination's conventions, so practice looks like the real paper rather than like generic quiz questions.
Read before you set
Check the questions and the scheme before putting them in front of a class. A generated question can be subtly ambiguous, and ambiguity in an assessment costs the student, not the tool.