Puppies are like sponges, they just soak up all the new information they are given, they love to learn and to please. You as their guardian have the responsibility to help them learn.

New experiences - people, places, sights, sounds they all count.

Lets put it into prospective - Would you send your 5 year old child to college?
I would think not (unless they were extremely gifted think sheldon off the big bang theory) 

You send them to preschool or nursery and then to primary school so they learn the basics first - right? 

So waiting until your pup is 6months old or older and then sending them to the groomers for their first visit is a bit like the 5 year old going to college, in many cases they are prepared for it and don't know how to cope with everything that is going on.
SO we need to start them young, and I mean as soon as they have had their vacinations and are allowed out into the world they need to visit a groomers, and yes they may not need a trim but they experience will help set them up, and many groomers now will have some sort of puppy package you can participate in to help your puppy become a confident canine. 

From first hand experience - puppies who are later coming to visit often are harder to work with as they have got into a poor routine at home where they maybe allowed to get away with things, like biting a brush or not settling and unfortunately this makes our job as groomers harder and instead of helping your delightful fluff ball have a smooth introduction we can be een as the bad guys , and sometimes for those unfortunate ones who dont allow guardians to brush them their first grooming experience will end up being a shocking sad expereince for all involved . And non of us want that