Sound loopy for volume service, and it's clear he's talking about straight
highballs, not "cocktails".
I can see a few arguments for it, like it sounded like a good idea in theory
(for someone who doesn't actually have to do it).
1 - it disperses the mix without requiring a stir
2 - First sip gets a mouthful of the floated spirit, which may create a
favourable impression (see
[Dan the Melon Man] "...and you're going to learn them all." )
3 - Pouring twice looks like you are adding more alcohol
4 - taking more care of the drink may look flashier.
OTOH, if I see a 'tender having to 'top up' their drink after adding the
mixer, it can imply they forgot something or didn't get the measurement right
first time.
BUT, in general it seems a non-standard and clumsy way of doing stuff, and
would be really annoying when actually trying to serve a busy bar. As you
said, getting consistant measures would be more difficult than usual. I think
it would slow you down with all the double-handling.
I couldn't recommend it in a working environment, but it may be some sort of
flashy service addition.
Could be worse, this ritual :
[Chance] Re: Club Cocktail Service also has (had?) it's
place, but doesn't translate into many working bars these days.
.dan.