I agree people should definitely take their sick animals to the vets.
But if the animal has a slight problem that is obviously not an emergency, then I think there's no harm on asking on here first. It might be something simple that can be solved without going to the vet.
Or more information can be gathered to give to the vet, because some vets mightn't know a lot about guinea pigs.
You could also call the vet and ask if it's necessary to bring the animal in. Sometimes the vet might say to just keep an eye on it for a day or two and the animal might get better.
Some people bring their animals to the vets for the slightest things and spend so much money, which I guess is their right and is the safest thing and gives them peace of mind. But it's not always necessary.
If a guinea pig isn't eating, drinking, is acting different like less active, etc. then that could be an emergency. But some things are not emergencies, so asking here first won't do any harm.
Especially if the vet is closed for the weekend, etc.