In case of nightly or continuous submission, there are no need to upload a new revision if extension metadata are matching.
Indeed, in that case the package are expected to be the same. In practice, a given extension generated for the same Slice revision/Extension revision/Arch/OS/... may be different if created a two different day. This could be explained by the fact year/month/day info are included in the package.
To prevent the upload of an extra extension revision when not needed, new item revision will be created only if submission type is experimental.