This is something I have a bit of experience with. Originally, I did one cycle... and then didn't do another for a couple years. I found that that one cycle definitely lifted me up so that I could go on to new levels, make higher gains, and reach a greater plateu. Then I did my next cycle after I had peaked out for more than a year and came up another permanent step on the ladder. After that I started hitting regular cycles 2-3 times a year... and sometimes for 5-6 months on at a time. I found that if I was in a range to make cumulative gains (which most people are) one cycle a year was an excellent stepping stone. Then when I wanted to make huge gains, lift VW's, and scare small children... more frequent juicing was needed.
If I was in my 20s, I would juice on the installment plan... one cycle a year.