Most common reasons mentioned:
1. one less thing to go wrong
2. eliminate a variable
3. useful RPM is above the end of the advance curve
4. don't understand what it does
16-18 initial. 35-6 all in by 2400 each engine will have its limits and needs with timing . if its racing, it never sees the low rpm's so no curve is needed. when locked out, it is one less issue to have to deal with and, it helps keep timing rock steady....