We've done some testing since we noticed the new form sharing options (which were not highlighted in any of the release webinars from what I recall). While good information is here
https://support.workfront.com/hc/en-us/articles/216668788-Creating-Custom-Forms I thought others might find this helpful:
1. Similar to previous settings, as long as the form is set to Visible System Wide, users can see it once it's been added. There's now more granular ways to share forms (users/teams/groups) instead of just groups.
2. In order to add a form, it must be shared with the user/team/group, and they must have manage access on the object with the form.
3. Once added, if View System Wide is on, then user permissions on the form are based on the object where the form resides.
4. If it's not Visible System Wide, only those users/teams/groups it is shared with can see/contribute/manage based on their access for the object it is on. This may be helpful if there is information that only higher level management should be able to see. This is now a good option to 'hide' sensitive information since you can't apply the same type of restrictions to form sections (just make a different form and give executives the ability to add it).
I did notice on the help page that it says when you share a form with a group it gives them capability to edit it under Setup which I thought was odd to be able to give that level of admin access just by sharing a form. However, when I logged in as another user with manage/add form capability, there weren't any options to access the form under Setup. Perhaps they're just referring to the 'object set up'/edit page where you can simply edit the form instead of under the details/custom form tab. Just wanted to mention it.