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Plants grown in pots that are too large are susceptible to root disease because of excess moisture retained in the soil

Not necessarily so Cheeser, how often one waters, how much, temps, and air circulation (off the top of my head) impact the moisture content in a pot. I've seen plants grown in humongous planters, more like a tree really...point is, it can be done safely as long as over-watering is avoided.

very good tip, thank you DB

You're very welcome Cheester, it's what I live for

In my experience having a pot that's too big causes several problems, the main one being once you give the soil a good soaking it will take ages for the soil to dry up. Giving you very long wet/dry cycles. This in effect smothers the plant. Having a fast wet/dry cycle gives maximum oxygen to the roots. This is often the most limiting growth factor when growing in soil. Get the wet/dry cycle correct and you get super fast growth. Have a small plant in a large pot with wet soil for a long period and growth will stop totally until it starts to dry out again

If using a big pot with a small plant, give small amounts of water until plant is bigger.

I wouldnt say that will give best results, best to just use the correct size pot. Giving small amounts of water doesn't give it a proper wet/dry cycle. This is important to rid toxins that the plant excretes. If you just top up moisture you don't wash these toxins out and you can inadvertently leave dry pockets that can cause root damage.

In my opinion pot size if very important

Couldn't agree more Jet, knowing what size to use, and when to transplant is a very important part of the growing cycle. Pot size affects so many growing parameters: watering, feeding, healthy root development, avoiding rot or other fungal diseases, the size and shape of your plants, how light is distributed, whether or not LST, HST are possible and so on.

I always recommend using 3-4 pot sizes during a plant's life cycle, ending up with something in the 3-5 gallon range, larger if space permits.

Cheers