Der_Echte has presented the basic facts. Balsa blades are great for hitting and smashing because of the characteristics of the wood. They are not great for looping so most top pros do not use a straight up balsa blade. I don't know of any.
One thing to note though, the Viscaria is listed as a blade with a Balsa core:
"Butterfly Viscaria: Koto-ALC-Balsa-ALC-Koto" (that comes from Ooak Forum).
And This is from the Butterfly site:
• Combines Arylate fiber features of lightness, flexibility, and shock absorption with the Carbon fiber features of high elasticity and minimal dissipation of energy.
• Koto outer plies & Balsa core.
• Viscaria's compact head size makes it ideal for quick re-looping right off the bounce.
So any pro who is using the Viscaria is potentially using a blade that has Balsa in it. But, in spite of the information presented above which comes from 2 different sources, I have heard many people claim that the inner ply of a Viscaria is Kiri. I had a Viscaria and know it had a Balsa core. But I have felt others that did not feel like a balsa core. So it may be that they made them with Kiri at some point. But with the ALC and the thin core, Viscaria is different than one of those Balsa blades that has a 5, 6 or 7mm thick balsa core.
My sense is, if you like hitting and smashing and you don't loop much, Balsa is fine. If you are looping most of the time, you will do better with something else. And reaching higher levels, at a certain point, in my opinion, is about developing your loop on both sides so that you can loop everything. At the highest levels of play, that is what they do, so you don't have players using one of those blades with a thick balsa core at the highest levels because they are really fast but not useful for looping.
The style of play that went with those kinds of blades has been outdated for the most part. Der_Echte also mentions the exceptions to that. Certain pips players. But I don't think the pips players who are really high level are using balsa either.
