Well, the question is what counts as "need". By my way of thinking, whether an important spare is worth carrying is determined less by how essential the item is than by how hard it would be to get during a long-distance trip. So, for example, when I owned a diesel, I never carried spare DEF, since you can get it at any truck stop or auto parts store. OTOH, the linear actuators in our custom-designed bed would be a real problem if one of them failed during a trip. So, I am planning to get and carry a spare, even though it will be a bit pricy.
This is mostly a pragmatic decision involving what you and your companion decide that you really "need". But, if you need it and can't easily obtain it, it is probably worth carrying.