"If at all" means that the condition you gave doesn't usually happen or doesn't need to happen, but CAN happen. With 'if' it emphasizes that the condition is unlikely to be true: Example: If he comes here = he might or might not come, I don't know If he comes here at all = he probably won't come, but hey, just in case he does . .
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.