Like @maitimo the Hotline Miami lock-on can be super handy, whether on PC or VITA or PS3.
For 3rd person-shooters of any kind I'll turn it off along with auto-assist, so long as the game never gets so broken I need to turn it back on or else redo sections a million times over (Hello, GTAV rampage missions!).
I used it in Hotline Miami because I played it with a controller on PC.
For Dark Souls, I definitely use it. It's part of the design. It's kinda of weird comparing Dark Souls lock on to other games, but I kinda see what you mean. For shooters, I turn it off or don't use it.
I don't even get why you wouldn't use it in something like Dark Souls or Zelda. It's not like in a shooter where it makes the combat trivial, it is simply allowing you to center the camera on the enemies in games that don't have strafing as part of the control scheme. In third person melee games lock on targeting is not an assist like in it is in shooters, it's just part of managing the camera and movement in a 3D space.