Disable Device is a skill reflecting your mechanical ability. Slight of hand is a skill reflecting your ability to take action secretly. They uses the Dexterity stat as a modifier.
What can you do with Disable Device & Slight of hand?
These are more skills that have existed for a long time in the game - though in older editions it was called Pick Pockets, Open Locks, and Remove Traps.
Disable Device allows you to disable or sabotage devices or open locks. Classes with trapfinding (rogues) can disable magical traps. Slight of hand allows you to palm objects or remove object from people without them noticing.
Which of these have ground for use?
I am not personally a fan of Disable Device, though by the assessment there is nothing wrong with it.
Pick Pockets, er, Slight of Hand is a case where a skill is almost certainly necessary because of the nature of conflict. It takes place under time constraints, against an opponent, has a serious consequence for failure, can't be modeled at the table and can model a partial result.
I have currently been running games where this Disable Device is not used, and disarming traps and opening locks depends on player skill adjusted for class almost exclusively. For an example of the system I've been using you can check out the Locks and Keys .pdf which is Zak Sabbath's system for opening locks with modifiers for thief skills and using the reverse of the system to disable traps..
Disable Device is another skill that can easily turn into a skill tax skill. The systems usually are only able to use traps to great effect till about level 8. It's mostly dependent on the ability of your DM to continue to scale the DC's correctly.
Slight of Hand works as is practically with no modification
What is it we gain by having this skill?
A quick simple way to determine the ability of a character to open a lock or disable a trap and a mechanism for picking pockets.
We also gain quite a bit of role protection for the thief type classes.
What do we lose?
As I've handled it in my games before, there is space for an interesting mini-game to replace this that relies on player skill. I also find that allowing each trap to instead work as a trick with various intractable parts can lead to much more entertaining results then simply getting it out of way with a roll. Allowing the characters to attempt to trigger a trap so they can pass or allowing them to disable it by clever thinking seems more interesting than a quick roll.
For those that have some anxiety about describing how traps might work, there are plenty of resources on-line. Not only my Empty Room, Tricks & Trap design supplement but other bloggers discussing trigger mechanisms and more. There are also plenty of ways to allow class selection and level to provide relevance to your ability to open locks and disable traps.
Very little in the case of Slight of Hand. The skills existence may cause the players to do things they otherwise wouldn't, but in the long run that may be a positive influence on the game.
Conclusions & Suggestions:
Either keep this skill as is, or develop an interesting mini-game regarding this skill that your players enjoy. Suggestions are welcome.