What drawings should or need to be done in a utility patent?

ANS: In general, according to USPTO rules, anything that will ever be claimed must be shown in a drawing. There are limited exceptions in situations where drawings add no value to guide/limit how to make and use what is being claimed (e.g., chemical formulations, biotech sequences, etc).  You should avoid adding figures/drawings that are not necessary because they will generally significantly increase your patent preparation and prosecution costs, including burning the examiner to go through superfluous disclosure material, possibly getting them annoyed.  That said, figures are useful/needed in a patent to the extent that they represent elements that are either are ever to be claimed, or are needed to enable/support anything that is to be claimed. Anything that is an obvious extension of an existing drawing, generally should only be described in the disclosure as alternative embodiments, not needing separate drawings. An important exception to that principle is when it comes to section 112 (f) "steps plus function" claims were even obvious routine method flows need to be shown in flowchart drawings to count as the required structures disclosure for the claim.