The reasoning behind the British switch to nighttime bombing was sound. Despite interwar projections that the "bomber would always get through" reality turned out quite differently. The RAF savaged attacking German bombers during the Battle of Britain, and British bombers on daylight retaliatory raids had a tough time of it as well. Losses were unsustainable, meaning that planes and aircrew were being lost at a rate much faster than they could be replaced. So the switch to nighttime bombing was an effort to reduce losses, as enemy interceptors would have a much more difficult time finding and destroying British bombers. It also led to decreased accuracy and increased civilian casualties.
The Americans began bombing over Europe in 1943. They were still under the impression that their bombers would be able to successfully make unescorted daylight raids. It was thought that the B-17 with its rugged frame and impressive defensive armament would survive where British bombers failed. Attacks like the Schweinfurt-Regensburg raid did hit German industry hard, but the losses the American forces absorbed were catastrophic. The daylight attacks had to be suspended until the Americans could rebuild their forces--and supply them with long-range escorts in large numbers. Planes like the P-51 Mustang and P-47 Thunderbolt were able to escort the American bombers to their target and back, destroying Luftwaffe fighters and keeping the bombers much more safe. They still took losses, but the Americans were able to sustain their numbers much more easily than the British, so it was a sustainable combat practice. (American production of planes and aircrew was simply staggering)
I hope that answers your question. Followups by OP and others are always encouraged.
As /u/Domini_canes says, daylight bombing proved unsustainable for the RAF and Luftwaffe early in the war, but the USAAF strongly believed in it. The key point, when both day and night attacks were formally agreed as a strategy, was the Casablanca conference of January 1943. Churchill was greatly concerned that daylight raids would lead to disastrous casualties, Ira Eaker of the USAAF produced a memo and presented it to Churchill, "The Case for Day Bombing", concluding "If the RAF continues night bombing and we bomb by day, we shall bomb them round the clock and the devil shall get no rest." Churchill was sufficiently convinced to at least agree to a trial, leading to the Casablanca Directive, a very broad outline for the RAF/USAAF Combined Bomber Offensive.
As stated, unescorted bombing did indeed prove unsustainable for the USAAF as well, but the introduction of the P-47 and P-51 finally broke the back of Luftwaffe defences from 1944.