Robert,
You ask a good and important question. Most folks believes as you stated that a bigger pot must be better. Once you put a plant in a pot, the dynamics of water flow changes. I won't bore you with the physics of that, but you cannot compare plants growing in the earth with plants growing in a pot.
Unnecessary repotting is by far the most common cause for plant failure. I have seen it happen hundreds of times.
When roots have lots of room to grow, the plant tends to put more of its energy into root growth at the expense of foliage and flower growth. More importantly, a large pot with lots of soil will retain water for a long time before it dries out properly. If that interval is too long, the roots will slowly start to rot. Of course that root rot is out of sight and goes unnoticed until it is usually too late.
A proper sized pot will reach the appropriate level of dryness for most plants within 3 to 10 days after a thorough watering. If it takes more than 10 days, then the pot is too large. If it takes fewer than 3 days, then it might be time to consider moving the plant up one pot size, although as long as you are willing to provide water every couple of days, it can stay in the same pot.
I have written an article on repotting that explains all of this in detail that I will email for free to anyone who sends me a request.
wcreed@HorticulturalHelp.com
Will Creed
wcreed@HorticulturalHelp.comMy website