I had intended to write pretty much everything Grant did - thanks for saving me the time Grant!

I will add one thing:

Actually those are a gold mine for me for the OPPOSITE reason - I often get huge performance GAINs from adding in the first two of those things. Temp tables can be used to split up massive join queries to get the optimizer better metrics to have more efficient plans in subsequent processing. And dynamic SQL can provide exact values for optimal statistics retrievals which can also lead to optimal plans (and certainly the dreaded nested-loop-with-a-kajillion-row disasters). I do note that this is an ADVANCED usage from someone who has been doing SQL Server relational engine design and tuning for going on 15 years now. 😉