An annual re-post -
Everybody has an opinion on pruning tomato plants. Here's my view of the subject.
First, I'll assume we are growing "Indeterminate" types of tomatoes, i.e. vine tomatoes as opposed to the tree-like ("determinate," aka "bush" tomatoes) ones often grown in pots. Left alone, vine tomatoes will grow 10+ feet along the ground, as you can often see in gardens in Bermuda, but we stake them.
Up here in New England (Yankeeland), we need to prune them because our short growing season doesn't allow much time for good fruit formation. We have to prune most of the suckers and plenty of their leaves, and we cut their tops off in July or August - all so they will put their energy into good fruit and not into further pointless growth.
Further south, diligent pruning is less important.
And even though I grow mine in fine soft soil, I fertilize them with liquid fertilizer whenever I think of it. I usually have lots of plants, but only ended up with 10-12 this year of around 5 varieties.
Here's the best site I have seen on indeterminate tomato vine gardening. For all of the effort, and despite our short season, it is well-worth it when you pick one on a hot day and eat it in the garden like an apple. A tomato should be hot, with little salt on it.
Image: Commercial tomato picking in North Carolina