Forgive me in advance if I am stating what's already obvious to you (the OP left some question as to what you are referring to).
I assume you are speaking of Chapter H, which contains the notes for each nationality's vehicles and ordnance. These include numbered "historical notes" and lettered "special rules" for that unit.
Which notes to use are listed at the end of each row of the vehicle or ordnance table. Each unit's special rules are stated under the lettered notes, though there is occasionally useful game information even within the numbered notes.
If Chapter H is indeed what you meant, then absolutely! These notes are not only useful, but are absolutely essential to many games. The notes provide unit special rules that often change how you employ a unit or even how you utilize your entire OoB. New or restricted tactical options can completely change tactical options and your entire strategy.
A few examples include:
- SRs for PRC
- MMC and/or SW included w/vehicle
- CA restrictions for certain armaments
- Mechanical issues restricting movement, Start/Stop, Bog, or ESB
Etc...
P.S. When applicable, studying both sides unit notes is (for most players, I expect) a major part of the preparation for scenarios w.