My main attraction to back locks over liners, comps, and frames is that it is easier to tell when your backlock is working positively and properly than with the others.
This is not an so much an issue when you can deploy your blade in a mindful, careful manner...but if you get distracted while deploying it's possible to start cutting without your blade fully engaged. That can happen with any lock type, but I've found the very positive *CLICK* of a lockback yields great tactile and sound feedback.
Maybe even more importantly, this holds true for blade disengagement also.
The detent and "snap" close on a back lock is very positive. I cut my left thumb very badly with a Bradley Air because I thought it had fully seated in the closing detent when pocketed...boy was I wrong.
Plus, it's possible for liners, frames, and comp locks to "work" even though they may be compromised by having a less than ideal lockface to lock engagement. You could be working away, oblivious to the fact that your lock up is not clean.
With backlocks, it becomes evident pretty quickly if the blade is "out of battery" because of pocket lint or grit, letting you know you need to service it almost immediately.