Impact gets more views and PPV buys from this. People are going to keep tuning in to see how Kenny loses the title.
That's what Impact needs more than anything, some new people watching it. Their hope is that this will bring in new viewers and that some will stick around once this storyline is over.
Impact needed a big match to do that. They couldn't make a big match out of their current guys and they can't seem to sign any of the bigger guys who would bring in viewers just by name. New viewers aren't going to tune in to see two guys they don't know, no matter how big of a deal Impact could promote it as.
With renting out Kenny, now you can create those big matches.
Kenny vs. Swann is a big match now. Kenny vs. Moose is a big match, or whoever else are their main guys. Because most people don't know who their main guys are, this is Impact chance to give all of their main guys the spotlight by having them challenge Kenny for the title.
Now it's on Impact to build somebody up or acquire someone who would be believable enough to beat Kenny.
I predict they will keep this going until July, when WWE's 90-day clauses are up, and they're going to resign Samoa Joe and then make it Joe vs. Kenny to be their ultimate big match, and then have Joe win it back.