Companion planting (from 2 to 4 vegetables grown together) is practised whenever possible. It is only made possible because work is done by hand.
Crop combinations are exciting to explore, despite their complexity. The good economic results obtained at Bec Hellouin are partly based on this practice, common among market gardeners before the rise of mechanisation. Each year we discover new combinations.
However, care should be taken not to mix the plants too much on the same bed. Four seems to be a maximum, because too much complexity increases the harvest time and can make the system unmanageable from a professional perspective. Polyculture can be carried out in a simpler way at garden scale, from bed to bed, without combining crops on the same bed. [Ed: But this does not take advantage of the last point below.]
It is advisable to keep a written record of crop successions for proper rotation management. This traceability can simply be achieved on a wooden board (chestnut) planted in the bed, which retains the memory of previous crops.
One of the attractions of companion planting is that for almost equal effort (soil preparation, fertilisation, weeding, watering, etc.), we benefit from several harvests instead of one.