They are high-yield and they come up frequently on step 1 exam. Do take the time to learn the cross-sections. I think organizing the cranial nerves into groups is key in helping you understand the structure of the brainstem and memorize its cross-sections.
*First of all, 1st and 2nd cranial nerves are found outside the brainstem.
*Cranial nerves 3(oculomotor n.) and 4(trochlear n.) are found in the midbrain. Midbrain is the upper most part of the brainstem and happens to be the shortest(only 2cm I think); and since oculomotor and trochlear nerves are both motor nerves they arise medially. Motor cranial nerves typically arise medially from the brainstem and this applies to both the pons and the medulla. So the rule of thumb is: motor cranial nerves arise medially and the sensory ones arise laterally.
* Cranial nerves 5,6,7 and 8 arise from the pons. 6 arises medially because its entirely motor. 7 and 8 are found in the cerebello-pontine angle and can be damaged by acoustic neuromas and menigiomas(important clinical correlate).
*cranial nerves 9, 10 and 12 arise from the medulla (spinal accessory n. is technically not a cranial nerve). CN 12 hypoglossal n. is damaged in medial medullary syndrome(because it's motor and motor nerves arise medially). Also don't forget in medial medullary syndrome, the medial leminiscus is also damaged because it's still medial; it ascends laterally through the brainstem but in the medulla it's still medial. That's why in lateral medullary syndrome you get loss of pain and temperature sensation(damage to spinothalamic tract) with no loss of fine touch, vibration and pressure sensation.
I know I didn't cover everything here and probably missed a few things but maybe this will help you understand brainstem anatomy a little better.