In the first year, especially if you started with rhizomes, you're better to just let everything grow. The only energy that rhizome has is what's stored inside of itself and it has to use that limited amount of energy to do two things, grow roots and also grow shoots. The roots will enable it to draw nourishment from the soil in the future and the shoots will enable it to produce additional energy to help sustain growth. Hops are very very efficient at being able to produce way more energy than what they need to sustain their top growth, so any that's left over ends up being sent back to the crown to be stored and used the following season. After harvest, being that the plants are still alive but really aren't making any new growth, any photosynthesis that's occurring will be used to allow them to blast off the following year. When the plant first takes off, those simple sugars can produce some really wild and uneven first growth (bull shoots included) which can lead to a lot of variability when harvest time comes as some will climb faster than others. Removing the first surge of growth at this time and training the shoots that come later will help with more uniformity at harvest. Home growers don't really have to be too concerned with this issue.
One other reason for cutting back the first growth is to help with disease control. I guess the overwintering spores of downy mildew will kind of hibernate in the fall buds that form (near the surface of the crown) and those are the first to blast off in the spring. If left to grow, the resting spores will begin the disease cycle all over again and provide inoculum for further infection as the season progresses.
There have been years that I didn't have time to deal with mine early on and I ended up removing the first two (sometimes three) flushes of growth of growth and still had good crops. Have fun and don't forget to beat 'em back into submission about every 3 years, they kinda like it!