Conduit is required for single-conductor wiring. As opposed to, example, 12-2 with ground. Even so, if it is in an area where it may be harmed, use conduit. Otherwise, it is just extra material that you are adding to your project for no reason.
The only time I have seen it not required is when using metal sheathed cable. If the cable is all inside one layer of metal then there is no way it can cause a circuit to conduct unless it is broken. So, don't worry about putting conduit on every single wire.
It is also useful to put some kind of covering over electrical outlets. This prevents small children or pets from being tempted by how beautiful the outlet is and either pulling out plugs or eating power cords. These coverings are called Outlet Protector devices and they come in different forms. For example, there are protective plates that fit over the outlet and contain a hole for the cord to go through, and protective tubes that surround the cord but allow access to the plug portion of the socket. There are other options too, such as special connectors that connect instead of plug into normal sockets but still protect them from small hands and pets' teeth.
Outlet protectors help prevent accidents caused by exposed live wires and they should be used whenever replacing old wiring with new wiring is done.
An NEC-accepted ground path is an RMC, IMC, or EMT. As a result, if the wires are in steel conduit, no additional ground wire is necessary. If they're not in conduit, then you must provide a ground wire to connect to something metal.
For example, if you were to use aluminum wiring, then you would need to provide a ground connection too. You do this by either connecting one end of a ground conductor to the metal housing of the device being wired (this should be done at each outlet), or by using a ground block.
A ground block is a metal object that connects to the chassis of a circuit breaker or fuse box and serves as a second ground point. It can be used instead of providing a third wire into the outlet. Ground blocks are available in different sizes and shapes for different applications. They're usually painted black to match the rest of the chassis panel but otherwise they can be any color you want.
Here's how to determine if there's enough space for a third conductor: First, count the number of outlets on the panel. Then add two more for a third conductor in case it's needed. For example, if there are four double outlets, then there will be room for eight conductors total.
Conduit, on the other hand, is needed for all residential and commercial wiring in some regions of the country, increasing the cost and difficulty of house wiring for the typical homeowner. Wiring without conduit is called "commercial free play" or CFC. The phrase comes from the fact that before 1965, there was no requirement by law that any part of the wiring system be enclosed in conduit. That's because most old wiring was done with 2-wire cable containing both an electric conductor and a ground conductor, which were not required to be separated until 1965.
Today, most new wiring is done in conduit because it is considered safer for people and animals to avoid contact with exposed wiring. Conduit also prevents damage to the wiring when tools are used during home improvement projects.
However, most existing wiring can be kept intact by using products such as Medusa conduits that are designed to be compatible with existing wiring. These products allow you to add new wiring while preserving what you already have so you don't have to replace everything at once.
If you want to add new wiring and remove existing wiring all in one project, then you should consider conduit wiring. This will help prevent accidental contact with live wires and will protect the wiring against damage due to tools and work debris.