I almost always put the skins in all my tomatoe products- stewed,sauce and paste. I have even heard that the highest concentrations of lycopene are in the skins.
For stewed tomatoes I will peel and put the peelings in the blender( I have a VitaMix which really pulverized everything) then add that to the whole tomatoes to cook down some.
For the sauce and paste I usually core and cut in half and dump them into a roasting pan sometimes adding peppers,onions garlic and spices, and cook in the oven at about 350. About every 45 minutes I will take them out strain the juice off and put them back in. Repeating this until I reach the thickness I want. Then let it cool and put it all (pulp,skins and seeds) through the VitaMix until I have a smooth sauce/paste I like this method because. The juice that I drained off gets canned too instead of being evaporated into the air. So I basically get two products from one. It great for soups or flavored rice.
By leaving the seeds in I save the task of removing them and except for a slightly paler color cannot tell the difference. Of course it really depends on your blender. Some work really well and others not so much. Do a test run and then run it all through a fine strainer and see what's left. You don't want pieces of peeling left , they tend to roll up and become like little fine sticks. You might have to experiment some with how many you do at one time.
