It depends where you're going to use it. The main failure modes are an open circuit and a short to ground (though intermittent connections are always interesting). The latter could be caused by the insulation melting/cracking/rubbing away.
In the cabin I have used domestic wiring without worrying (including in the living space of a camper conversion).
In the engine bay I wouldn't trust the insulation. For a run strapped securely away from heat/oil/coolant/screenwash you could probably get away with it indefinitely (e.g. to repair corroded lighting wiring) but it isn't a great idea especially if the circuit is even remotely safety-related. You also have to consider abrasion.
Other more-or-less exposed bits of wiring such as powering a reversing camera off the reversing light circuit are an intermediate case. Realistically the cable can probably withstand the conditions but I wouldn't splice a length into something important because of the risk of abrasion somewhere you wouldn't notice it.
When making this judgment call remember that many accessories use whatever cable was going cheap when they were designed (and not just the cheap add-ons). Your brake lights (for example) don't.
Don't forget that if you add a length of cable in parallel with something important and that length shorts, it will blow your fuse. Taking the brake lights example again, say you add a high brake light to a vehicle without one, and the insulation cracks when cold where it flexes for the boot hinge. It then shorts to the bodywork, next time you use the brakes, the fuse goes and you have no brake lights at all. The failure is unlikely, but the effect of the failure is severe enough to not want to take the risk.