Many beginning prosodists treat metrical variations as though they were vermin: find them, identify them, then ruthlessly exterminate them. But variations are neither good nor bad in themselves; they are only prosodic tools. All that matters is how they're used and whether they work. When you've noticed that Shakespeare's
What studied torments, tyrant, hast for me?
What wheels? racks? fires? what flaying? boiling?
In leads or oils? what old or newer torture
Must I receive, whose every word deserves
To taste of thy most worst?
is not perfectly regular, your analysis has only begun, not concluded. Too often, though, I see "critiques" which are little more than lists of metrical variations, as though they were spelling errors, and the critic had performed some regulatory action by ferreting them out. I usually respond with some reference to Milton's
Rocks, Caves, Lakes, Fens, Bogs, Dens, and shades of death[,]
since critiquers are a tad hesitant to claim either that every other word must be stressed or that Milton didn't know what he was doing. (They may think, "If only he'd had access to The Gaz," but they aren't quite brave enough to say it.)