To put it simply, a sheet can be used faster. Internet speeds vary from user to user, so it's easier and less time consuming to copy/paste an image as opposed to downloading a file at the mercy of your current download speed. They're often easier to evaluate during the approval process, as well. It can also promote more specific asset organization.
ZIP archives are more appropriate when a submission has a large file size.
ZIP archives are more appropriate when a submission has a large file size.