Do I plane already cut wood?

[PRSpoggers]

Hey yall, so I got a planer (winsor no. 33 hand planer) and I have white limba for a neck and honduran rosewood for a fingerboard. My dad who is helping me with this project is telling me not to plane the wood since it was already cut. I went over the wood a few times each just to plane everything up. Do I need to plane the wood that was already cut? Thanks

[curtisa]

You plane the wood if it needs it. Just because it's been supplied cut doesn't mean it's flat.

If you rest the wood against a known flat surface, does it appear to have any gaps underneath it? Can you rock it by pressing diagonally-opposite corners or from one end to the other? Do the surface(s) you require to be flat have a rough unfinished texture? If the answer to any of the above three questions is 'yes', then you probably need to plane it.

The action of planing is to ensure the surface of the timber is on the same plane, ie that it is completely level, flat and smooth. Timber bought from a supplier may be cut with the intention of being flat and planed, but other things may influence how that timber reacts to the environment once it has been cut free from the original slab. It may develop some degree of warping, cupping or other deformation that results in the timber no longer being perfectly flat, in which case you plane it to restore the required surfaces to being as flat and smooth as you need it to be for your application.

[Bizman62]

In addition to @curtisa's list, you can also use a straight edge to see if the wood is flat. Using a light coming from the side can be very helpful with that: If the blank is flat you should not see any light in the shadow the straigth edge casts. That has to be checked in various locations lengthwise, widthwise and diagonally. Sounds more tedious than it is, it only takes half a minute to check every direction.