Depending on what you’re wrenching on, an impact socket can be used in place of a normal socket when using a normal (non-impact) ratchet. A hand ratchet will connect and drive an impact socket just as it would with a normal socket. Similarly, it is safe to use an impact socket on a hand ratchet (although not vice versa). The main concern is going to be tool clearance as impact sockets tend to have thicker walls (and thus larger outside diameters), although in most instances this issue won’t come into play. If the impact socket will fit in the area you need to drive the fastener, it will certainly work in place of a thinner walled normal socket.
Speaking of wall thickness, you’ll notice that the average impact socket has a wall thickness that is approximately 50% thicker than that of a normal socket. This difference is most significant in the corner of the socket, as this is the location where the socket wall is the thinnest. The thinnest part of the socket is normally there first place where stress cracks would develop due to forces placed on the socket during use. Beyond the thickness difference, the impact socket is made of a more ductile, i.e. softer, material that is specifically designed to absorb the impact forces from an impact wrench. While these things are interesting and good to be aware of, neither of these differences affect your ability to safely use an impact socket on a hand ratchet.
That said, we do want to take a moment to note that you should never use a normal socket on an impact wrench as this presents a serious safety concern. Considering the thinner wall design and generally more brittle steel used to make normal sockets, they don’t absorb the impact forces when driven by an impact wrench very well and tend to fail catastrophically under the heavy stress. When they fail, they tend to send metal flying, which can obviously be very dangerous to the mechanic or anyone nearby. As such, it’s important to stick with impact sockets when using an impact wrench.
Conclusion
All in all, impact and normal socket definitely have their respective purposes with regards to when and where they are best used. That said, it is important to use them as designed. While either can be used on a normal ratchet, make sure to only use a good set of impact sockets when using an impact wrench to ensure your safety. Happy wrenching!