Greg Esres wrote
Can anyone suggest any reasons why you shouldn't use GPS or DME to
lead your turns when approaching a fix, such as an IAF, on a non-GPS
approach? (Meaning that you don't wait for complete reversal of the
nav instrument.)

The AIM has a couple of requirements for a "complete reversal" of the
TO/FROM indicator, but they aren't instructions about how to fly an
instrument approach. Regardless, those injunctions may be outdated in
a GPS world.

Yes, I can suggest a reason. What you are proposing is very precise
and very easy, and unless one is careful to maintain proficiency in
doing it the old-fashioned way, it will lead to a very insidious form
of GPS dependence.

In fact, I generally do what you suggest in real life because:
(a) ATC RADAR is not good enough to tell anyone I'm doing it, so I
don't care too much about the legality - and in any case, like you I
can't find anything regulatory to say I can't.
(b) It allows me to become established much more quickly and
precisely.
(c) It's just much easier to anticipate the turn than it is to wait to
cross the fix, and then wind up with a needle out of place that has to
be returned.

This is all great until the GPS goes TU. Suggest you goole r.a.ifr
for a previous thread on the topic: GPS Dependence - more insidious
than I thought...

It's not exactly on point but covers a lot of this same ground.

Michael