If you use the lockdown as your go to half guard game it can breed a tendency to give up the cross face and letting yourself get smashed while trying to get double under hooks. Which is unfortunate because sometimes you can prevent the cross face, hip out, and get into an offensive half guard position while bypassing the entire lockdown series.
That being said, when you do get flattened out.. the lockdown is probably the most valuable half guard you can have. I use it like a worst case scenario guard when I get smashed and flattened. I'd rather get the underhook, hip out, and drive into the guy while he's trying to pass my guard but most of the time, that just won't happen.
Like any guard, it has it's place, it's range, and it's optimum set of circumstances. The reason why I gravitated to it so strongly was simply because I was getting smashed so damn hard when I started training. When your flattened out, cross faced, and getting smooshed into the mat.. that little outside figure four and grapevine becomes a life saver. Then, to take such a horrible position and to then use it as a position for offense... mind blowing. You only have to hit the electric chair once on a dominating wrestler to appreciate the value of the lockdown.