We've just started doing this at my clinic, for multiple reasons.
1.) We're able to get the bloodwork results first thing so the client isn't waiting around after the appointment is over for the results.
2.) Some owners don't like to see their dog's blood drawn, especially if we have an issue with the dog bleeding afterwards/having to poke multiple times due to wonky veins.
3.) Some dogs need more restraint than a simple hug to be safe for a blood draw. Although we are in
NO way mean to the dogs, we are much more liberal with what we do when we are away from the owner. Most owners become upset with what they view as "unneeded" restraint, especially if their dog is screaming/growling/biting and clearly unhappy with said restraint/procedure. We have to keep everyone - and that includes the dog - safe, and a thrashing dog that we need to poke with a needle and draw blood is
not safe. So while we feel comfortable muzzling and holding down a dog (at times needing multiple people) away from the owner, it would probably upset the owner if they saw us do so in the room.
If you are a new client, we don't want to chance 2 or 3 happening, so we remove the dog from the room and draw blood in the back. If you are a frequent client, we know your preferences/dog's attitude, and we tailor our approach to suit the client/patient (and we have quite a few dogs that MUST have their owners either muzzle them or restrain them for us, or the dog would probably have to be sedated to get anything done).
Just giving you a tech's perspective.
Mini Vent: this especially bothers me with nail trimming. I wish people understood that the time to desensitize your dog is NOT when you expect the staff to have the procedure completely done in 10 minutes! We had a Boxer come in for a nail trim who had never experienced it before. He was okay for the first foot with our cooing and treats and pets, and if it was a training experience we would have stopped then, showered him with the treats we were dolling out, and helped him on his road to thinking nail trims are awesome. As it was, we had to do ALL the feet (that is what the client is paying for) and by the end of it the dog was being restrained by three people and on the floor because after that first foot and a half we passed his threshold and he just couldn't take it anymore and started flailing/trying to bite. It turned into an ordeal, the dog was extremely stressed out, and he will probably have to be muzzled/restrained excessively for any future nail trimming ventures. Ugh.