P J I don't use the slicker on big peices like saddle seats, but use it on most all small projects and especialy on things that have to fit exactly. Stamping will swell the leather and slicking it will cut down on that. Special projects that require the best grade of stamping will get slicker treatment. Also some of the best leather in a side will not need slicker treatment because it's allready real firm ( the butt and a foot deep strip right up the backbone about to the halfway point)
Bigger stamping projects that can't swell at all because of fit get contact paper on the flesh side before stamping. Small items like sheaths you can use shipping tape on the flesh side. Use it just prior to staming and peel it off just after.
You want the leather to be a little wetter than when you stamp when you slick it and the moisture should be clear thru the leather for best results. Then lay it on your bench untill it dryes to perfect stamping case. ( it's called casing the leather when you get the moisture right for stamping)
You can play with scrap to find what perfect case is for krisp stamp impressions.
It will also brown when the moisture is good.
Different tannery's leather take some playing with to find the perfect case for stamping. Hope this helps. Robin