Often as a designer you'll come across some odd/bad request from a client. More often this request is at the last minute or the worst possible time in the project time line. How and when should you "save the client from themselves" and adversely when should you put the designer ego aside and just do it?
As a designer you have a vested interest in making sure your clients look as good as possible but sometimes it's just out of your hands. Last minute inane request, color changes or redesigns often have you pulling your hair out and asking "why". The best bet is to ask questions... and lots of them.
"Is there a particular reason you wanted this change?"
"What do you feel you'd benefit from making this change?"
"Do you realize this may back up the deadline(s) and are you concerned about that?"
instead of simply :"that's a horrible idea"
By trying to get in their heads and find out what made them decide to make the change you have a better understanding and may, just may, be able to sway them in a different more beneficial direction. Or come up with a better plan of action all together. Letting the client know of the ramifications on their scope and project timeline will often detour them from outrageous adjustments.
Some clients simply won't budge - "I said do it, so do it". As long as you clearly understand and communicate with your client even when they go against your design expertise at least when the the project comes out "not so good" you gave it your best effort to ensure the quality of the project. Always try and educate your client first and try to keep personal preference out of the equation while trying your best not to talk down to or belittle your client. They'll appreciate your input more if you do so.
The primary key here is understanding what the client needs and why. Often you'll find an answer by simply running through it in your head and having a short educational conversation with your clients. This is why it wont' work or may destroy an otherwise perfect layout. Sometimes by going back to comp stages and trying it out visually you can easily illustrate the pros and cons of changes and often you'll quickly find a comparable solution. Take the time to listen and educate - you'll be less stressed out than you think.