Client: "Make this line of text fluro pink, I like pink. And the background yellow. Yeah! Yellloooww. I like pink and yellow."
Designer: "Pink on yellow? Mmm.
Client: "It's more important than that other text there"
Designer: "Ah, I see what you're going for. But.. Pink on yellow will be a bit strong and hard to read because of the low contrast—in fact, it'll probably be ignored because of it... Why don't we go with a rule in the margin, between this column and the one next to it? Nothing big and bold, something subtle and gentle – it'll grab attention without being too over the top, which means people will be invited to read the text. We can also make the heading a red, which is your corporate colour, so it links in with your other branding materials as well as the rest of the book and will grab attention to this text, which will clearly be important because of it.
Client: "You're awesome, have more money"
The good designer asked why, discovered why the client was making their request and turned it around. Sometimes the client has no real reason and the suggestion disappears into the ether. Sometimes they're just masks for an effect or emotion they are going for but can't articulate.
Sometimes this senario happens in my work. It's not just good designers who will ask why?