Short answer

If you can, you should definitely avoid it: It’s horribly expensive, takes an awful lot of time and is really difficult.

Longer answer

In case you’re working in safety critical systems, like medical, pharmaceutical or avionics, you are most likely required to provide traceability.

One nice hook for traceability within arc42 are blackboxes within the building block view: You can use the arc42 blackbox template to document:

• the requirements fulfilled or satisfied by this particular building block,
• the source code needed to implement this building block.

to be done: crossreference to blackbox-template