That you'll put everything that
I think it's better for the website.
But if you say you're going to do feature X and Y and change Z because of reason ABC, and as a consequence you'll say the website will be 10 times better, then hopefully we'll have some metrics to discuss.
10 times better could mean more conversions, a faster/more secure checkout for an e-commerce website, or just a prettier brochure one.
These kind of statements are too vague on their own, you have to put some meat around to show me why it'll be better.
But hey, sometimes you have to make the sale. If the clients are paying and they're happy after the project is complete, then there's nothing to worry. It's marketing and advertisement working.