Powder-separated molds (whether using mica, talc or something else)
are quite easy to use and separate. For pretty simple,
straightforward molds, I like using that approach. Unfortunately,
you can't always control where that parting line will "rip" as finely
as you might like. If that line isn't on a flat plane, I think
you're probably better off with a cut mold.
Also, the peaks and valleys that you see in hand-cut molds help the
mold "lock" together better to avoid any slippage when injecting it
with wax. (That's why it's done that way.) You do put mold locks
into place on powder-separated molds, but typically only at the
corners. So a hand-cut mold locks all over.
Finally, it's my understanding that you cannot do a powder separation
with the new silicone materials -- that it only works with the
traditional "rubber" molds. Fortunately, the silicone cuts really
easily and smoothly.
There are many on the forum who have been making molds much longer
than I have, so there may be some other perspectives I haven't
thought of... I'm looking forward to hearing them!
Hand-crafted artisan jewelry