A good question Hogman!!! I actually know quite a number of martial artists...(seasoned variety)..that prefer latchless Balisongs. This is certainly not globally true, and most of my friends are involved in the Korean varieties..(Hwarang Do, Tae Soo Doo, Tae Kwon Do, Hap Ki Do, Yu Do, etc.).
I'm also not sure this would hold up across the Korean Domain, so maybe some other guys will kick in some information and experience. I'm 54, and some 25-30 years back.., I actually preferred latchless, although I don't now. The latch integration has become profoundly better obviously, and I think it is sort of a non-issue for true combative use these days (simply my opinion).
For all-around use, there are certainly many advantages to having a nicely designed piece with a latch (a whole topic in itself).
As for "locking"...the lock is your grip with a latchless model, so a truly fine piece designed to be latchless is a must for defensive purposes.
I actually haven't talked about the latchless option for many years come to think of it. Seems like all the highly sought versions are merely for collection these days..., but I do have a few highly skilled friends that carry Balisongs with no latch.
"Hunters seek what they [WANT].., Seekers hunt what they [NEED]"