The difference is one is an assistant and the other is a tool. Essentially a tool, has one function. The outcome of all inputs is clear, once you learn the tool. An assistant, behaves different in different environment, it anticipates and interprets. It may not be deterministic. It's easier to use but harder (or impossible) to understand.

For example, the lasso selection in Photoshop is clearly a tool. A "content aware" selection on the other hand is an assistant.