People posting a UI glitch or being frustrated that a feature has been removed without warning does the following:
Brings it to people's attention, helps them recognize if it's a widespread problem or just an issue with their hardware or installation, and for anyone who hasn't 'whined' they can learn that whatever is wrong with their device isn't intended.
People whined about their phones slowing down as their batteries aged. The result? Battery replacement program. Keyboards. Speakers. Display lamination, etc.
You know what doesn't help? A smarmy reply saying "things change, deal with it!" or "they'll fix it next time" or "I don't see a problem". It shuts down discussion. It discourages exploration and discussion. if your only excuse is that 'it's an opinion' then it doesn't serve a purpose, does it? Otherwise all threads would be:
"Hey, I have a problem."
"I don't!"
End.