“With” Expressed by Maʿa versus Wāw

Al-Mafʿūl Maʿahu: Accompaniment and Coordination

جِئْتُ أَنَا وَزَيْدًا: zaydan is an accusative accompaniment complement after wāw.
جِئْتُ مَعَ زَيْدٍ: maʿa is an adverbial in iḍāfa with genitive zaydin.

Both mean accompaniment but use different syntax. The second is an added teaching comparison.