First, MiB tells Sawyer that he wants to get off the island and that the island doesn't need protecting.
Second, MiB sends a message telling everyone at the temple that they can join him in leaving or stay and die.
Third, MiB tells Ben Linus that he is leaving and that he needs Ben there to take care of the island.
These are what MiB has stated of his motivations. I think we can confidently settle on the fact that he wants to leave that damned island. This has been a consistant factor in all of his actions and motivations. But what he is not telling us is what he needs in order to leave. This leaves a lot of open holes in his motivations. Recruitment has something to do with it.
There is one discrepancy in these motivations: him telling Sawyer that it's just a damn island, and him telling Ben than he needs to stay and protect the island. Either he is playing both of them, he is playing Ben, or he is playing Sawyer.
Whoever he's playing, the fact is that he's playing somebody, which raises the question: why? Does he need Sawyer and Ben particularly on his side, or is he merely trying to get as many people on his side as possible, regardless of who they are?
Here are all the possibilities I can think of concerning why MiB would need these people in order to get off the island:
1. Sacrifice: He needs to sacrifice a certain amount of lives (not likely)
2. Imbalance: In order to lift the restrains, he needs complete control of the islands inhabitants, leaving Jacob with no control. He needs to tip the scale.
3. War: Jacob will try and stop MiB from leaving, so he is building a big army to make this not a problem.
4. He doesn't: MiB doesn't necessarily NEED all these people, but a. he is doing them what he believs to be a favor by getting them off the island or b. he is evil, and is trying to corrupt as many souls as possible in his escape
5. Functions: All these people have predestined functions and/or roles that will play into his escape
6. Manipulability: The more people he has on his side, the more people he will be able to control and manipulate, the stronger he will be. It's just practical.
Any more? Why do YOU think he needs these people?