I consulted a Teamcenter expert and he described the use of 'required' checkbox to me like this:
Required checkbox is a sort of fine graining of Teamcenter quorum. For example: In your workflow select signoff team, you would like 2 out of 3 reviewers to give a signoff. you should set the 'Required' flag for the reviewer (one of the two or both reviewers per my example) who must give signoff or have teamcenter wait for it.
To me 'Action Perform' radio button displays the kind of review available depending on your selection in the resource panel (the left side bottom panel in your screen grab).
My explanation above is based on what was observed in Teamcenter. There seems no documentation (in TC 11.3) for these 2 options, though GTAC closed a PR on this subject stating that it is fixed in TC 11.2.3.