When we give in to the temptation of giving a positive spin to our stories we are effectively denying the God that we claim to be serving - it's that serious.
Much of this is the Christian equivalent of spin and corporate business talk. Meaningless except to those schooled in the jargon.
With Luke writing positive stories about Paul's work, Apollos decided that he needed to engage a publicity firm to get his message across (no he didn't).
By promising big things, we are usurping God's role in mission. He is the one who brings growth, not us, and we need to avoid making any claims that suggest otherwise.