When I was helping at the Tomatomania events, I was frequently asked about pinching and pruning tomato plants – whether to, how to, and when to. My response was “It depends whether your garden is on the coast or inland.” If on the coast, then some pinching of blossoms and shoots at nodes is wise, to promote better air circulation and enable more direct sun onto the fruits. But, if the garden is inland, then pruning is a bad idea, aside from pinching blossoms for a month following transplanting.
Here’s why, in both cases.
Do Pinch Off Blossoms – For A Month After Planting
This is the case for all tomato plants and all garden locations, since it’s dealing with establishing a strong plant that will be very productive.
Pluck off all blossoms and any fruit for at least a month after transplanting, until the plant is at least two feet tall so it’s forced to direct its energies toward establishing a strong root system. If blossoms are allowed to develop fully and then set fruit, the plant will expend its energies on fruit production at the expense of establishing a strong plant that will be able to produce many more tomatoes. This is the case whether the plants are "determinate" (they grow only to a determined height, set their blossoms, ripen their fruit, and then the plants die), or "indeterminate" (they keep on growing and bearing flowers and fruit until killed by frost; although they may poop out before then due to lack of nutrients or warm-enough weather).
Whether To Prune Plants Depends on Where The Garden Is Located
The concept of pruning plants is an East-coast and Midwest thing based on two environmental conditions there that we have somewhat on our coast but the opposite inland.