I would agree with Darangal's description of other people's energy being like junk food or a sugary caffeine drink - you can get a quick fix, but you won't necessarily like the results. You can easily pick up another person's needs, habits, focus, behaviors, vices and other psychological patterns, good and bad, and I can't say for sure if these can be "filtered out" to only select the "traits" you desire. I remember when I 1st tried the method Catpottery described:
Visualize a tendril emanating from your spleen chakra toward your target's spleen chakra. In between this, visualize a filter to keep any bad, unwanted energies out. Then, suck them dry.
I used this technique when I was 15-16. I connected to the guy's 1st 2nd and 3rd chakra with tendrils and started draining for a couple of minutes. I thought he'd be a good candidate for this because he was apparently strong, young, well built, athletic etc. In the next couple of weeks I felt that I picked up his tastes and habits - for example: never in the past did I enjoy fast food, or too much alcohol, or cigarettes, but I started feeling this gluttony and I'd eat more in a single meal than before.
My, let's say "corporeal desires" also increased, and I was feeling very in tune with my body. In a way, I became more material(istic). I think my overall energy became denser (or of "lower frequency", lower grade).
His "energy sample" was like a perfume I was carrying for a while, which had a certain impact: Women liked it and they responded significantly better to me (which was one of the main reasons why I started this experiment in the first place), I enjoyed doing physical stuff more than ever before, my (physical) senses became sharper and people felt my presence was "stronger" and they would court me more. The way my environment treated me was certainly better.
At the time, I didn't bother with wondering if this sort of operation would have any lasting effects on me (or on him), or if it would wear off after a while. As long as you inject yourself with another person's patterns, you are preventing yourself from expressing your true nature, because you are expressing their "borrowed" nature. This is all only my interpretation of one of my experiences, and is in no way an attempt to give advice or tell others what they should or shouldn't do.
Harvesting is an interesting topic and I'll return for a part 2.