This debate is entirely about whether the Tories are up to the job.
I think it's more about whether the conservative MPs want to keep their well-paid jobs. I doubt that many (if any) will vote to say that their own party is incompetent. With the active support of the DUP the vote seems a foregone conclusion.
Any Conservative MP who voted against their own party would likely be de-selected by their constituents for the next election (whenever)
So the only effect is to give Jeremy Corbyn the chance to say that he tried to do something, and to reduce the available time to discuss Brexit.