You must consider the line you use in any lacing. But, the Butterfly is great in many lines. It can add midline eye, add multiple eyes at one point, be used to isolate a weak part of line, even bend several lines to one.
Mostly it is used as a single eye, in a single line. But, it must be dressed correctly, is best if the eye is loaded last and less, and that the 2 ends of the line are loaded about the same. Each end pull is the lock, and equal pulls give least unbalance/deformity. The eye is also best, if it is to be loaded, to be pulled perpendicular with the line, and not inline/down the line's length.
Prussicks are great too; but when whole line is loaded, is not the same when only area 'above' prussick is loaded. When the area below prussik is not loaded, the prussick sits on a tensioned/skinnier line; on top of a 'shelf' of the 'fatter' unloaded line below it. When the whole line is loaded, the area below the prussik can become 'skinnier', and not have the shelf advantage against slip.
i advocate using both hands at different positions for final tightening on MA jigs. Seek a point of pull for 2nd hand that is just on other side of primary hand pull from first pulley that that hand pull goes thru. Seek to place all body weight on primary hand pull, then pick up on that 2nd hand pull, giving 1xBodyweight + 2xeffort as inputs. Thus, get body = 4xEffort on zRig and body + 8xEffort on a '5:1'. Impacting as input is also possibility, especially when you have 1 force (body weight) to keep load in check, and then can impact with other force(effort) (or reverse), or both impact at same time.
A slack line has no sideways resistance (it moves giving up distance instead of building power/tension as distance x force is applied); so a slack line can't be leveraged with perpendicular force. But, a tensioned line, does resist sideways force, reducing the distance/ building tension in response to force applied. Thus, we can leverage a tense line like this, then also feed that as input into the zRig etc. for another type of final tightening etc.