Means "use of" or "used for purpose x". Your sentence means "In the restaurant, there are separate tables for smoker's use."
喫煙 + 用 = Smoker's use
舞踊用の衣服 Clothing for dancing
管理用 For administrator use
調理用 For cooking
Or the the word can be used by itself meaning "errand, task, business."
何かご用がありませんか?Is there anything I can do for you?
何かご用ですか? What can I do for you? / Do you need something?