"How does "defragmentation" work on a Mac?
Is this what "repairs" means?"
Works on the Mac drive same as on a PC drive.
You need an app like "iDefrag" to do this.
"Repairs" are entirely different. For basic disk checking and repair, use "Disk Utility".
Contrary to what some may say, you DO want to defrag a drive if you're recording audio or video to it.