If shoudln't make much differance as long as the pivots are all stable, one side of the bridge would only lift more than the other if the pivots were deformed in some way.
The aim with installing the springs should be to equalise the string tension, so obviously if you've got a very unusual string guage on you may want a bit more spring on one side to the other but this would normally be acheived using the spring claw.
Maybe his vibro block only has 4 holes and be just wants 3 spings, or maybe one of the spring holes is damaged?
this wouldn't make any diff at all - in one side vs the other for spring positioning.
you just have to have some stability against both posts which are the fulcrum of the tremolo. if you had only two springs down on the low e for example it would be lopsided and would likely hurt the guitar against one of the poles.
Some take that middle one and put it diagonal which spans 1 or two spots in the hooks.
What does matter is the amount of springs -
I am not an expert here, but this seems pretty simple.
the more metal you have in there the more rigid the movement is going to be. It's also going to be a bit more consistent and lends well to heavier guage in strings..
if you have only a few springs in there, it will be more sringy/spongy or easily moved by control of the bar and string bends. It also exposes a curve on the amount of tension control past a certain point off of the center point - like, once you have the bar depressed a quarter of the way down, the rest is easier..