An associate lawyer I know shared this little nugget with me. Once, when she was just starting out, her cell phone rang early on a Saturday morning. There weren’t any deadlines coming up, and she couldn’t for the life of her figure out why her boss was calling her. When she answered the phone, he only gave her a cryptic: “I need you to get in here.”
She of course got dressed quickly and sped through several traffic lights to get in the office as soon as possible. When she arrived, her boss passed her in the hallway. She said to him: “What do you need?” His response? “I just think you need to be here working on Saturday.”
We both agreed that of course if he had something specific in mind, it was reasonable to ask her to work. The point is, there was literally nothing going on. She was begging for billables and he wasn’t delegating any tasks. She sat there and cleaned her office for a little while and then went home. Ridiculous!
Recovering Paralegal 
I have this exact same problem. Except I’ve stopped answering those calls now! Good to know it’s not just me!!