The answers to your question of timing are extremely broad, and deep. (I'm physically exhausted from digging a trench for a new yard hydrant, so I'll ramble on about the topic while I'm resting).

Timing depends on your goals, and will be different depending on what they are.

Fruit trees for example, are best grown short to ease harvest and other ongoing maintenance. It's all about the fruit, not so much the esthetics of the tree, so there's a lot more pruning. Usually a major pruning while dormant, then a second summer pruning once the fruit is set to thin and eliminate redundancies.

With ornamentals & shade trees it's about esthetics.....and coexisting with said plants. Dormant pruning is almost always the best timing, and almost always encourages maximum rate of growth. You can also see the structure of deciduous plants much easier when dormant.

If mistakes have been made in plant selection or placement, and you want to instead limit growth, then pruning during active growth usually has the strongest limiting effect.

(I'm not a proponent of sheared hedges or formal topiaries, but they have their own unique set of rules and can be different depending on many factors).

Sometimes you temporarily keep branches that you know will eventually be removed, in order to strengthen a young tree. For example I planted a Pistacia chinensis this spring that has a really bad narrow crotch angle on one branch, but I will leave it until the tree is dormant so it can feed the tree during the growing season. I will not however allow this branch to grow much, keeping it headed back.

The existence of flowers and or fruit is highly dependent on proper timing. Most bloom on old wood (Rhododendron), and timing is critical. Others bloom on new wood [Lagerstoemia) and are more forgiving. Lilac (old wood) is the poster child for improper pruning (if flowers are the goal, and if they aren't, why a lilac?)

Every single year I see big old lilacs being heavily pruned in late summer-winter-early spring, which eliminates the flowers. Prune right after flowering ends and you get flowers the next spring.

Deadwood is always best removed as soon as it's noticed. Same with all growth coming from below a graft.

This topic is vast, could go on forever, but I'll leave it to others for now, back to digging trench!

The late Cass Turnbull of Plant Amnesty fame is probably your best bet for further education.