The really truthful answer to this question depends on whether or not you plan to pull a permit thus require an inspection by your local government and/or prefer to install it to current electrical codes.
If you DIY, and don't plan on anyone ever seeing what is in the crawlspace, then running your wires in a conduit is your choice.
The argument against conduit is heat, which will be generated in high power delivery and be retained in the conduit.
Also, it may depend on the crawlspace layout, note that conduit is not required in the space behind the drywall.
However, if you go to sell your house with the HPWC still installed, a sharp home inspector should call that out, but it's possible may go unnoticed.
Also, should you ever have a fire in your home, whether or not related to your HPWC install, Homeowners' Insurance may deny your claim if they notice that.
For you it is done, but other"s may want to check with local codes, which I suspect requires conduit, as I did for both garage attic and drywall surface mount to get the permit.