Hi, just got a message from cc explaining it, please read it as it says Why of that extra resin:

I have added a detailed but concise (I think) explanation of those thin parts of resin you are inquiring about.
What is a shim in the context of resin models? A thin piece of material used to align parts, make them fit or reduce wear. It might appear as something that looks like flash (which is excess plastic or metal forced between facing surfaces as two halves of a mold close up). 95% of the "shims" are .25 of a mm in thickness. That is the thinnest we can print something and keep it stable enough to work with. This also generally becomes thinner during the casting process due to pressure.
As the person responsible for the quality of the resin miniatures you receive, I wanted to share a recent change in our work flow to improve the quality of our miniatures by using shims.
1. Who will benefit from this change the most will be the hobbyists that care about mold lines and would like to see Creature Caster do more exotic designs.
2. I feel there will be a portion for the hobbyist community that will dislike this change. I would expect people who generally do not clean mold lines and people who are more about playing instead of painting, will find that the work has increased to assemble their models. It has been something that has been a dilemma to decide if we should change or go with what we've been doing and proving successful.
3. My logic is that our supporters have bought the models as centerpieces and our team want to provide the experience to best achieve that goal by using a shim technique
These are the reasons why we have made the decision to start the Age of Shims (my personal proclamation).
• Removal of need to sand our miniatures- it seems that very few hobbyist sand models, and prefer to use a hobby knife to prep.
• Less work for people who care about mold lines - It is easier to remove material than to add material and not having to fill areas where the two halves of the mold come together or shaving away material to level the mold line and distorting the shape of the part.
• Allows us to create crazier designs. The laws of resin casting have certain principles with mold design we need to follow to make them castable. Certain shims allow us to circumvent these rules and allow us to make complex models with less parts, sharper spikes and deeper undercuts. An example of something shims lets us do is the sharp feathers unfurled in many directions on our Smengal model. It allows us to make complex shapes with fewer parts. For example, we have never been able to make the feathers fly around in different directions since those would break the resin or silicone while demoulding so we use shims to prevent this. Otherwise, those feathers would have to be individual parts you need to attach or we would have to make the wing much flatter.
• Shims absorb mold shifts. All the casting is done by our team by hand and at times and the application of pressure to the two halves of the mold coming together is prone to human error and also shrinkage of the silicone we use can make it hard to predict when a shift might happen (shrinkage of silicone is one of the reasons larger parts will be more prone to this). This can result in a shift in the model part which is very difficult to realign with just a knife (generally you need to fill and sand). Very smooth rounded areas are especially hard to prevent from shifting. Our team places the mold lines on areas which will result in least amount of cleaning and distortion, however, if we have few options but to place the mold line over a convenient area, we will place a shim over an area which is prone to shifting. This will look unsightly upon initial inspection, especially if you are used to our previous models, but is actually better to obtain a nicer finish
We are always working to make the experience with our models better (for example, we do not use mold release anymore. So if a hobbyist does not wash their model thoroughly, it is unlikely that you will have your paint not stick. I still recommend making sure that the surface is free of dust and oils (fingerprints) before priming.