My rule-of-thumb is to glass anything that's thin, punctureable, or has seams ie; planking.
The cloth is in the resin to impart strength, like rebar in cement. Over the hull planking it has a sort-of shrink-wrap effect, holding things together, such as when seams in the planking open up due to the wood's expansion and contraction.
The keel doesn't need this sort of back-up, it basically does that job itself, but it should get well coated in resin. Inside the hull ought to get resin coated as well, even if it doesn't get cloth.
The point is that any water that gets into the wood will be adsorbed making the wood swell, which can pry things apart in extreme cases. It also may not have a way out and will cause rot and mold.
In the attached image, that crack in the seam is in the filler putty under the glass. It's not visible inside the hull, and it's not an issue at all because the glass is intact. The cloth here is 4oz which you can see the weave of in the reflection of the flash, with poly resin. The second pics is just the rest of the boat 😉