It is used as a way of expressing "even if there's any other way possible".
"I'll have 3 drinks tonight, if I drink at all." (if I drink anything)
"Drink alcohol in moderation, if at all."
"We seldom see her, if at all."
"If at all possible, would you please go to the store for some lemonade?"
"Do you have five dollars?" "I have five cents, if I have any money at all."
Hope this helps.