SwiftSyntax tries to minimize the use of existentials (aka. protocols spelled with any or protocols spelled without some) wherever possible. This is because when the stored value is more than 3 words (a word is the size of a pointer) large, these existentials store their data on the heap. The data stored inside RawSyntax is larger than 3 words and thus every time you pass a value around as a e.g. an ExprSyntaxProtocol, a new heap allocation will be made and that data needs to be reference-counted, which causes a very noticeable performance overhead.