you can launder things but it will not change the value at all and net you zero profit, both pay the same amount for treasures just sell them directly to a fence, for anything useful use immediately or launder it.

It sells for the same price as you Launder it for.

I only launder items like Ingredients, Recipes, Motifs etc. I might launder some items I would normally sell if I used up my Sell limit and had some room left in the Launder limit. That way I can break even by selling the laundered item to the Merchant down there.

I heard, but have not tested, that if you launder a stolen piece of gear you get better inspiration on decon (the same as if it was a mob looted item). However normal stolen items give such low Inspiration it is not worth taking them to the crafting station, probably why I never tested this.

Laundering is also useful for items (like motifs and recipes) that you can sell in a guild store for much more than you can vendor it.