Depends on what bombing you are concerned with and at what timeframe. Since you didn't mentioned if you were interested on the strategic bombing on resources/industry or on civilian areas.

I highly recommend you read this book if you interested on this topic. The person wrote it was a professor I had and has given talks to the United States Air Force on his research.

You will find generalized answers to your questions in the reviews. https://www.amazon.com/Collapse-German-War-Economy-1944-1945/dp/0807858501

This is a difficult question to answer directly, because there is no strong consensus amongst historians on the moment which Germany was surely defeated. Some people will answer the moment that they declared war on Poland, others might say the moment they declared war on the US, some might say Stalingrad/Kursk/Overlord/Bagration whatever. Without a consensus here it is difficult to say how much strategic bombing had led Germany to that point, and how much it contributed afterwards.

One consensus historians seem to have, from both sides of the argument, is that strategic bombing did not really become effective until 1943 and 1944. Max Hasting's Bomber Command and Richard Overy's The Bombers and the Bombed are two popular narrative history books which are both highly critical of strategic, especially against civilian targets: Maurice Dean's The Royal Air Force and Two World Wars (1979) makes the same claim despite being pro strategic bombing. So if Germany had definitely lost the war before the 1943-1944 period, and strategic bombing was not very effective before then, then it was both unnecessary and a tragic waste: this is essentially what Hastings says in the conclusion of his book. That would be the end of a short answer.

In brief, there were two types of strategic bombing: precision bombing, intended to attack particular installations or centres of economic activity and put them out of action; and carpet bombing which was based on the concept of dehousing. Earlier in the war British officials believed they could dehouse up to 1/3rd of the German population which would cause such a crisis that Germany would capitulate. Neither types of bombing were as effective as their proponents claimed: precision bombing often failed to find the target, and sometimes the target was put back into operation quickly, and dehousing simply did not demoralise the Germans as much as the British hoped. An example of precision bombing would be when the RAF tried to destroy the Peugeot factory at Sochaux - they failed and dropped all their bombs on surrounding villages accidentally instead. The factory was later put out of action by the Special Operations Executive with 0 casualties to anyone.

In contrast, there are some examples of carpet bombing being succesful. One commonly cited one would be from Adam Tooze's Wages of Destruction which claims that in March 1943, the British campaign against the Ruhr industrial area stopped Albert Speer's potential revitalisation of German industry in 1943-1944.

I will put to you two perspectives that aren't often found in history books. The first is that if Britain had been able to direct the economic activity that went into producing its frankly huge bomber fleet into producing tanks it could have made a mechanised army big enough to invade Europe on its own: this is an argument made implicitly by David Edgerton in Britain's War Machine. However, any contemporary account of the Normandy operations will show you that even by 1944, the British had practically run out of men. They were at a breaking point for manpower and that was without fighting a multi-million man campaign on the mainland before 1944. Bomber Command was relatively cheap: it cost only 40,000 lives during the whole of the war. So while the British might have been able to turn 10,000 heavy bombers into 40,000 Cromwell tanks, and the bomber crews into tank crews, it may not have been able to fight for very long before running out of replacements. This is a gross simplification, but the point I'm trying to make is that while a huge air fleet could instead have been a huge mechanised army, that mechanised army would have run out of men, whereas Bomber Command never ran out of men. A small addendum: by 1944, Germany was devoting 1 million men to the air defence of the reich, as well as thousands of fighter aircraft and dual purpose anti-tank/air guns 88-mm guns. Without a bomber campaign these would have been redirected at either the Russians or British or put into factories-farms.

The second is this: strategic warfare is a much larger bracket than simply bombing. From 1939 onwards, despite committing comparatively few troops to the field, the British Empire fought a war in which it was massively victorious against Germany: an economic war. It blockaded Germany from the air and sea, practically sank the surface Kriegsmarine and forced the Italian Navy to port, and where foreign commodity orders could not be stopped directly, it out-bought the Germans on auction markets, buying things it didn't necessarily need in order to stop them from falling into German hands. At the same time it carried out commando raids the length and breadth of Europe forcing Germany to station large occupation forces. It infiltrated saboteurs and weapons into Europe. And ... it also bombed everything in Germany. I would view strategic bombing as part of the broader strategic war, and in this part it was indispensable, as a weapon to strike the enemy when there was in fact no real political, military, or economic alternative.

I'm sorry I omitted the American experience from this, as I have very very very little knowledge about that.