A loose cable like in the photo above gets caught in the spring mechanism of a pull down folding ladder at the attic opening and frayed.
Is conduit required in attic.
It is not required by the nec in a residential attic.
Using conduits will ensure that your wires are kept together.
Damaged cables can cause a short circuit or even worse arcing that will start a fire in the attic.
I once knew of a town that required all residential circuits be run in conduit.
It will be easier to repair wires if there is a short in the line.
For this reason the nec has protection requirements for nm cables in an attic.
Conduit also protects your wires from exposed surfaces such as rough bricks in a basement.
Always check in with the local building code authority.