Anytime you are through bolting you need a someway to distribute the load. For bolts typically you use a washer, for higher loads you use backing plates
Wood is great at a lot of things, but not at resisting the type of loads from through hulls. First you have localized compression
across the grain that can lead to localized deformation. Secondly you have minute shifting of the bolts that over time can damage the wood, particularly if using bolts and not studs (only threaded at the very end).
Backing plates help minimize both of these problems. The localized compression
issues by spreading the load. And the movement issues by, we'll spreading the load. And for very minimal cost. Figure a few dollars in parts
and a few minutes in labor. To me it just seems shortsighted not to use them.
Btw it's only 6:40pm here.... So no worries.