Talc is good cheap filler, it is harder to sand than the west 411 and 410 fillers. It finishes to quite a hard surface finish (but not quite as hard as west 403 or calcium carbonate). It can be used by itself or with other fillers to add thixotropic qualities (wont run on vertical surfaces). Or even to make a very sticky glue.
Talc is also the main component of most body fillers. Added to resin for fairing and smoothing fiberglass laminations. When applyed to resin it makes a smooth, creamy paste. Let it sit for an hour before adding hardener and using.
When using talc alone add 2 parts filler to 1 part resin