We need the flexibility in making validation rules on save as well, a lot of issues we have is allowing users the ability to save a form and continue it later, the problem comes in when they click submit and it triggers our workflows. We don't want them having the ability to save after that.
If they go back in and edit form it allows them to still save form even when workflow is running which causes a major issue between the time the workflow executes. We haven't found a solution or feasible workaround for this one so we try to limit how often we use the save button.
Having rules to hide save button and/or create validation rules against it would be nice. In addition hide the submit button would be nice to to avoid creating all these validation rules to stop users from editing after the fact. We do combine our automation with item level provisions or if they don't need to EVER edit we'd just give them rights to contribute only and not edit or delete but that isn't always the case.
Sometimes they just need to edit when it's in a certain "status" of a request. Just makes it difficult at times when we don't necessarily want to do item level security to achieve this since workflows can fail at times. It's alot of extra work when if we could control this on the form then regardless if they had "edit" rights, the form would not allow them to make changes if a SUBMIT button or SAVE button wasn't available for them to click.