Performance impact of "optimizing" spec file

[Herrick19]

Hi,

I am curious to know if there is a benefit in term of performance by doing these "improvements":

1- If there are a lot of "$ref" to responses, parameters and schemas in a definition file, is there a performance gain to dereference all of them to create a "flat file" where no more "dynamic" lookup are needed ?

2- Is there any gain in term of performance/memory consumption to strip down a spec files of everything that is not needed ? For example, examples, descriptions, text documentation, webhooks, tags, etc

3- Is there a difference in performance by using yaml vs json ?

I guess all of there answers probably have a "hidden" subquestion:
4- Is the specification file parsed only once at startup or is it parsed on each request ? If it is parsed and "compiled" at startup time I guess all these potential "improvements" would have a minimal impact since every single request after wouldn't be impacted by the initial loading time

Thanks in advance

Best Regards