Some background & context

When including third party logos, we often get given low quality files. Mostly these are low resolution JPGs, but I have seen badly hand drawn scans (expected to be used as is) or even photos of old stationary.

Recently we were given a folder with all the variations of a logo in a number of formats and sizes. Great! But. There are a lot of variation, some of which have only very slight differences, a lot of file types, a lot of sizes and no usage guidelines. So it's not always obvious which to use. I don't have the files to hand to count but there was probably at least 40 different files.

Another example: I worked on a project for a company who wanted a main logo with a variation for each department, then for each of these a horizontal version with the full company name, website and tagline, a square version with just the logo and website and just the logo.. Then for all of these a PDF, an EPS, a low res JPG, a high res JPG, a low res transparent PNG and a high res transparent PNG. All the variations were sufficiently different and they did (in their opinion) have justification for wanting all the different file types so this isn't as bad as the first example, but I did think this was too much.

My question - How many variations is too many? (or too few)

Note: By variations, I mean all the final files you deliver, so all actual design variation (e.g. horizontal / vertical / square variations, 4 color & monochrome variations, size variations etc) as well as all file types (e.g. EPS, JPG, PDF) and sizes (e.g. low and high res JPGs)

I always at a minimum supply vector and bitmap versions of the logo in full color and monochrome. Assuming no specific requests, is this enough? Should low-res versions be supplied, or is relying on the client to downsample the high-res version ok?

Size variations are also needed (sometimes?), for example, simplifying complicated shapes for showing the logo at smaller sizes. Should this always be done, or only when absolutely needed?

I understand this depends on a lot of factors and varies for each project, but should I try to keep the number of files to the minimum essentials or supply as much (as is appropriate and within reason as I can?

Edit: This question - How Many Directions / Concepts - is about initial ideas and concepts, I am asking specifically about finished work and the final delivered files.

This question - Logo Pack - What should I include? - is very similar, but more general. I believe the reasoning behind the question is different.