I am also in agreement with this. If you're only interested in a quick hurry up and give a decent result mockup you can plunk down huge chords and run with it. However, if you want the pristine real sound it is most certainly easier to achieve one part at a time. I was working an accompaniment this weekend (and prior) and initially I had plunked down the parts at the same time (played violins 1 and 2 at the same time on the same track). I then decided this weekend to play violin 1 in, then created a new track for violin 2. Recorded that line in live while playing back the violin one part (I should mention I had done my piano solo prior to this so I had a performance track to follow). The results were absolutely stunning compared to the plunking chord style! Because I was able to have each track manipulated by their own velocity crossfades and expression changes. I didn't duplicate the same patterns on both tracks so it gave them both their own individual sound. Not to meantion, that it gave a real and natural quantize to the song because I naturally came in a little sooner, or later than the previous recorded line of Violins 1.
The chord style works nicely in certain areas of songs when it's nothing but sustained background filler. However, if you stray from that and start having them harmonize one another, I think you might find it hard to beat doing individual performances. Not to mention the amount of editing you will have to go back and do to create realistic attacks, cutoffs etc. which I was able to produce instantly on the fly for each part. Being a bit redundant, on my prior performance song I recorded my 4 part chords seperately instead of block styled on one track and the results were so superior I have decided to no longer do it that way. It takes a little more time up front, but the results it gives me in one pass is absolutely 5 million times better then the days I would have spent quantizing, editing velocities etc on every note to make them not sound synthy. Besides, there is absolutely no way in real life every player of every section of the string orchestra can simultaneously crescendo at the same time (speed, attack/bow strength etc.) You will have late bloomers, early risers, even if only to a degree. Doing them seperate gives each section it's own life and distiguishable beauty. If you had plunked 4 notes at once in violins and raised the xfade, it would be to perfect. Which in essence would come across synthy and false to your ears (at least to mine). But as ALWAYS, if it sounds great it is great! Not everyone's going to agree with me, so do what works best for you.
**EDIT - I also should have mentioned, that this is specific to legato/sustained to me. Because during staccato and other short performance articulations VI Pro handles everything perfectly for me (it randomizes the humanistic playback, you can change each patch to have a slightly different delay, panning etc). When it comes to those fast styled performances I find it easier to chord style them (just as you see in the cool VI Pro videos) and it saves me TONS of time.
Maestro2be