I have been researching this question for some time now and the only reasons that I can find for cutting back the first shoots are
1. Control Harvest timing
2. Belief that this practice will have a positive effect on harvest results
Notes - This practice seems to be confined to the PNW / colder growing climates
I have had several creepers (late stage runners that went up a nearby fence) that heavily produced cones with very few leaves. The leaves that these sleepers had were small...very small compared to the gigantic leaves the main plants normally produced.
I also had a couple of first year nuggets that were not cut back, that by the end of September produced 1lb of dried hops each.
There may be something to the practice - however its going to depend on your climate. The PNW I believe, tries to keep them cut back till the first of June or right before then. That would kill my plants here as we are experienceing 70 degree days and lows in the upper 40's and lower 50's. I have 8" buds exploding from all plants of all 10 varieties. Ill do my first harvest around June 14 -cut back and then get a second harvest in September. I expect at least a lb (dried) from each plant per harvest.
So even if early pruning does increase harvest - lets just say that it does for the purposes of this conversation - by 50%. that means Ill get 1.5lbs from a plant per season. By not cutting back and accepting the lower first harvest but allowing a second harvest I get 2 lbs per plant per season.
So in order for this practice to make sense - cutting them back would have to increase thier cone production by 100%. I have seen no evidence that early pruning would produce this kind of result.
I have cut back a number of plants to test this practice and by the end of the year there is no difference in production between plants that were pruned early and those that were allowed to grow.
There is also another little fact that up until I started transplanting a few weeks ago seemed like a no-brainer.
While transplanting my 100+ plants to new beds this year I started cross referencing root size to production.
Most people (including myself until I started transplanting) believe that the bigger the rootball the more production of the plant as there are more nutrients stored in the rootball for cone production.
This is factually incorrect.
Root size/mass has
nothing -
repeat -
nothing to do with cone prodution.
My biggest producers are Nuggets. I had 10 2nd year plants and 7 first year plants. The first years did just as good and for 2 of them that got a new fert treatment I was experimenting with did much better. As I was digging them up I noticed that the 2nd year plants had rootballs 3'wide and 3' deep...the first year plants you could still hold the original rhyzome and they had 3 to 4 roots maybe 10" across at best and about the size of pecils. BUT they did have an amazing amount of micro roots.
This result was extremely consistant across every plant of all varieties and when you took this information and crossreferenced it with each plants production it became clear that production- in the context of root mass/size - has no meaning. The biggest producers had the most micro roots not the biggest rootball.
So when your talking production "Size Doesnt Matter".
Cheers
Edited Below -
First year Nugget - no cut back - each node were full of these - plant produced 1.07 lbs dried