Tokøta from Mastering.com walks through Logic Pro's Arpeggiator latch sub-modes, showing how each one changes what happens when you hold or release notes while composing.
Reset restarts the chord pattern fresh every time you play, while Transpose (the mode Logic drops you into automatically) lets you shift a held chord to new notes for quick harmonic movement, though it won't follow a diatonic scale on its own.
Gated Transpose works the same way but cuts off the instant you release the note, which suits percussive or performance-style parts more than sustained ones.
Add and Add Temporarily let you layer extra notes into a running arpeggio, with Delete Last to pull them back out. Add Temporarily works well for holding a drone note while building a melody over it.