my .02 on this topic (good topic BTW) is that some flies are greatly enhanced by the loop knot, others don't need it. So the advantage applies to only a subset of the flies you fish. Unless there is some other advantage I don't know about besides increased motion to the fly?
The disadvantages include double the tippet for the fish to see (I know I can see them a lot better), a weaker knot than say a palomar, increased wind resistance, susceptibility to imperfections in hook eyes (although I have seen them fail by 'opening' up which indicates a fault of the knot's strength).
Since I switched to Tiemco, Daichi, and other high QC brands ($$ I know) the eye imperfections have become a rarity not to mention the chemically sharpened points. Mustads are a great value, but I won't risk my precious few steelhead, salmon, cow striper or bonefish opportunities on a cheap hook.
Anyway, I am a straight palomar knot kind of guy, with a clinch now and then - only when the tippet is so short a palomar would put the blood knot to the taper too close to the fly and the fish are breaking so I don't have time to replace the shortened tippet.
Yesterday I started the day with a palomar knot, hit a sequence of hard fighting stripers in an inlet, then sight cast on the flats landing stripers up to 33", then landed a medium sized bluefish in the 6-7 pound class w/o steel, all on the same knot. After the rare blufish landing the tippet was hosed but the knot is still on the eye of the fly.
When I used to fish trout a lot and went to fine leaders I stopped losing those hard fighting holdovers to popped knots on spider-web fine tippets by switching to a palomar. Haven't switched back since.
On the down side it takes a little more tippet to tie a palomar than an improved clinch, although much less than a loop knot takes. Also people who haven't practiced it a lot get a curly-cue effect from over-tightening when drawn shut. It's possible to impact no pressure on tippet if the loop is drawn down correctly.
Anyway, the best thing to do is to fish with what *you* have confidence in, everyone's needs and opinions vary to some extent and within their target areas they might be 100%. My observations over the years have led me to the simple approach of using on super-tough little knot called the palomar.