I've yet to have a nailed frame fail so why faff around with glue, whether you use gimp pins or a nailgun
If you're making frames in bulk, the glue can be applied to lots of sidebars at once and whilst also nailing with brads (vertically through the top bar) is perhaps unnecessary it does help stabilise the joint whilst the glue sets up, and it's very fast.
I'm no slouch at nailing frames together, but using a 10-frame jig, glue and brads is still faster for me over the ten frames (yes, I am sad enough to have tried it a few times against the clock to check
). I imagine that using larger jigs would make the difference even more obvious.
If you're only doing a few dozen frames then quite probably it's immaterial what method is used, but if you're doing hundreds or even thousands and your time is money (or perhaps someone else's time is your money) then I suspect glue/brad nailing wins.
Having pondered on it, I suspect the reason for using glue and brads together might be that assembling frames in a multi-frame jig forces the brads to be put in vertically (I've seen it done differently, but it looked pig-awkward) and alone that wouldn't make a strong joint because the side-bar can just pull away otherwise.
I can't really see any benefit to using glue/brads over hand-nailing if frames are being assembled one at a time.
James