Are you referring to the internal lock that comes on most newer S&W revolvers? If so, you'll likely get a lot of different opinions as the lock has long been a very controversial issue amongst revolver afficionados. I personally don't find it to be a big deal, but I don't use it either (the lock-equipped S&W's that I've owned all had their keys stowed away unused in the box).
As to making the gun "misfire," there have been some cases of the internal lock engaging during recoil and locking up the gun's action inadvertently. These cases are, however, extremely rare and mostly endemic to lightweight scandium-alloy frame guns firing powerful, heavy recoiling cartridges like .357 Magnum and .44 Magnum.
All that being said, I personally wouldn't use the lock in the manner you describe simply because from what little bit I've fiddled with them, they don't really seem like something you could quickly and easily disengage under the stress of an emergency situation. Also, the keys to the S&W lock are not unique to each gun so anyone who has a key can use it in any S&W revolver. Finally, while the lock may prevent someone from being able to immediately fire the revolver, it will do nothing to prevent someone from stealing the gun. A small digital or biometric safe would, IMHO, be a much better option.
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