One is to evaporate saltwater from a source like the ocean or dead sea. This is then strained to a degree through filters, but there will be some things left in it. If your pool salt bag says something like 99.0% pure, like this one, then that is probably the process used. So there are some contaminants in there, but not a big deal.
Another method is to get salt from a salt mine. In this case it does not contain the contaminants of the salt water. So these will list something like 99.8% pure, like this one here.
Your filter should take any of the contaminants (i.e. broken down shrimp) from the salt water salt. Could it add to some buildup on your salt water cell? Not sure. I went with the purer salt to set up my pool as the total cost difference was pretty small.
I used aquasalt for my initial fill and at my local pool store it was only slightly higher than getting the less expensive and lower %age at the big box store. I have only used my pool store once for testing - that was before I found TFP, but like them in general. Their prices are good and they do not push anything. Of course prices can vary quite a bit at stores.