There is not much negative to say about Lemon Balm, save its desire to grow and take over the world. It is a cousin of mint, you know, and it grows in a similar fashion. Though mint grows wild and untamed, lemon balm sticks to more of a bushy habit. Beware though, it can spread. In my gardens, I am happy to give lemon balm a bit of free reign. It works well as a hedging plant and as a fragrant deterrent to garden pests in the vegetable garden.
To grow lemon balm, buy just one plant and split it into 2-3 smaller divisions. Allow them to grow all spring and summer, then harvest the leaves before they flower. In fall, split those 2-3 plants into more if you want to multiply your plants. Plant immediately and they will come back next spring in most zones. Right now, my lemon balm still looks like this: