the reason i never discuss that is because its a complex question depending greatly on the post casting production that will be required on the piece.
If i am simply producing a piece that will be cast and finished directly i usually allow around 1.5% to 2% to allow for the small shrinkage that happens at cast time, but if its going to be vulcanised and recast the cats really out the bag, and up the tree, with the wifes best bacon bits and the pastors wig...
cutting masters and allowances in the original model can vary greatly with as many iterations as their are jewellers. rubber moulds have linear shrinkage for example so scaling has to be directional as well as general etc etc etc.. but metal mould processes are completely different again.. so .. no easy answer im afraid ....
too complex to cover in a single mere post, and a great many boos on lost wax casting cover all these issues