I believe it can make a difference in performance, depending on the type of image used for emulation. Although, I do not have any proof that would support such a theory.

the cue or ccd are not only unnecessary, but it seems can no longer be used. i don't even know if the nero extension can be used. as for the others, i've found that it doesn't matter in the slightest. i've found nothing that plays on one format if not another, or none that play better in one format over another.

the type of image means nothing really

an image is an image

the difference will be like the difference between brands of photocopiers
they all copy it and can be read fine

They are all the same quality, it's just the file type some programs won't be able to read.