Great question, False! Seriously. The main premise that companion planting came from was 'like needs make good partners'...something like that. Birds of a feather...? Different species that enjoy the same pH, the same amount of water and sunlight, the same formulation of fertilizer the same Zone of habitat and temperature.
Plants love to be cuddled up with other plants. There is a fine line where all plants are getting their needs and sunlight as well as having air circulation between too many plants and too little resources and air circulation.
This also includes planting certain Genus together such as brassicas; cabbage/broccoli/brussel sprouts/cauliflower. These plants should not be planted in the soil they were grown in for at least 1 year best is 2 years. Solanaceae is another headache for 'rotation' practices in the garden; the tomato/potato family. To extend my garden real estate I use pots to grow tomatoes and cabbage and this year I have to plant potatoes in pots...always always always using sterile potting medium for any plant in a pot. I am careful to dump out used medium into specific beds or into my compost pile and consider the year of rotation. This helps to eliminate big diseases such as tobacco mosaic virus and early and late blight spores.
Companion planting has gotten off track because of garden mythology which has become rampant these days. I've not seen any science that explains why marigolds 'protect' other species from certain insects. Lining the perimeter of a plant bed with marigolds is very pretty but I've yet to spend any time or real estate on what I feel is foo foo gardening. And the marigolds won't do well planted with lettuces for instance. Flowering plants need to have lower nitrogen in relation to phosphorous and potassium or they won't flower. Lettuce needs at least equal proportions of N P and K or bolting will be earlier and faster.
There are other companion planting 'tricks' such as planting peas or cucumbers with corn using the corn for supporting the vines. This needs to be done carefully so that the vines do not suck up all of the chemistry (nutrients) the corn will need. Corn is planted first, in some areas they plant it in the fall. The vines are planted after the corn is 2 feet high.
Hope this helps. Lots of people think planting certain plants with other certain plants creates a symbiosis for some reason or another. Perhaps there are instances where there is scientific reason to plant two different species together for mutual benefit other than common sense reasons. Then I shall weigh the benefits of the combination versus the expenditure of my garden real estate.
The real reason for companion gardening is common sense. Group like needs together to get the most out of your garden real estate. Neighborhoods.