Well, with respect to the Soviet Union it was either attack them before they are ready, or wait until the Soviet Union is ready and fully militarized after its purges, and decides to attack Germany on its own.
As for the Western Front, it probably would have been better to actually attempt Sealion, rather than the Battle of Britain. All the BOB really did was strengthen the British Resolve, and decimate the Luftwaffe. Had those resources been spent actually attacking, or maybe even more to the Battle of the Atlantic instead, things might have gone a bit differently in that regard.