Companion planting means side-by-side. There are also risks involved with growing in the same space the following season mostly from disease transmission. My garden is small enough that rotation is difficult and some crops have to be close no matter how "combative" certain plants are to each other. Often one crop will deplete nutrients the following crop needs so a balanced fertilization plan for your soil is a good idea.
Companionship is a great theory but following this in practice is difficult and most do not notice much problem.
