"Sealing the chain" as you say, is indeed important for scenarios such as lookups within a loop. If you haven't .ToList()ed your lookup LINQ var, you will be re

"Sealing the chain" as you say, is indeed important for scenarios such as lookups within a loop. If you haven't .ToList()ed your lookup LINQ var, you will be requerying with every iteration. A simple change that can slow down code dramatically.