In Othello, why does Iago want Roderigo to "put money in thy purse?"

Iago is an extremely clever villain. He wants to carry out
his plan to ruin Othello by using other people to do his dirty work for him, thus
avoiding the chance that someone might cast suspicion on him. He almost succeeds. He is
so good at what he does that people even call him "honest
Iago."

Roderigo is one of Iago's pawns.  Iago knows that he
can use Roderigo's desire for Desdemona to help him bring about Othello's demise,
promising Roderigo that once Othello is out of the way, Desdemona will surely want
him.

So, he tells Roderigo to save up his money (which is
what he means when he says 'put money in thy purse') and follow the army to Cyprus.  He
thinks it will be easier to be rid of Othello when they are away from Venice, and he can
use Roderigo as a scapegoat. Of course, this does not turn out well for the gullible
Roderigo. He spends all of his money and ends up dead anyway, stabbed by his good pal
Iago.