You know how I often call my dog "evil hound". Given a choice she'd rather not have a bath and she puts on a performance that she hopes will induce me to save her.Hey, that's asking a lot of dog isnt it? How much support and guidance can i offer out of sight? seems odd. Why insist on my being out of sight, i genuinely dont understand??
The groomer is better and more comfortable with dogs than she is with humans who try to help their poor distressed dogs. Some even offer advice... Even I do that "she's giving you the death stare - be warned"... And I sometimes get in the way - ie the flow gets interrupted when the groomer tells you to move so she can reach the next bit.
There may even be an element of protection ie if the dog finds the grooming process threatening - the dog may try to protect the owner from it and attack the groomer. I just trust that my groomer knows what works best ie dog has no hope of "rescue" from me, actually she does but she hasn't tried screaming yet.
I rate it on a par with crating evil hound at agility comps and club training. If yelling worked - she'd do it. But what it gets her - is covered up and then she calms down. Ie so owner in sight - can cause the dog to be more excited and difficult to groom than if owner not in sight.
If you think about what the majority of SWF owners are like - if I was the groomer I'd ask the owner to sit in the waiting room too.
I don't think I'd want a groomer who insists on owners being elsewhere, because I'd want to see what the process is and how she gets along with my dog and how she deals with the bad behaviour (I can hear her...) because not all groomers are equally skilld or and some use aversives like yanking the dog around or slapping it. In which case I want to know so we can leave before the groomer gets chomped.