The other reason this is stupid is, the person reading your resume is usually either some administrative person doing basic filtering or a knowledgeable technic

The other reason this is stupid is, the person reading your resume is usually either some administrative person doing basic filtering or a knowledgeable technical person. Neither of them are going to be swayed by you claiming you increased user engagement or cut costs by X%. The administrative person is going to ignore it as it's beyond the scope of what they're doing, and the technical guy will laugh at it. I can't imagine a situation where this would realistically make you look good. Maybe if you're applying to a small/micro company who has no technical staff at present time, and the owner is non-technical and looking at your resume themselves? Basically a company that lacks anyone qualified to evaluate you, and they're looking for their first developer to build something that will help their business. Then you might be able to sell yourself by claiming you improved business metrics.