Stranding??

I’m fairly new to needlepoint and i need help understanding stranding. i know what it is and how you do it; i dont understand why or when to do it. i saw a post from earlier on here about using DMC floss for needlepoint, and everyone in the replies were saying they would strand it and use less than the full thing. are you supposed to do this with all threads?? i feel like dmc floss is already thin? how do i know if i need to strand a certain thread? thank you for any help sorry if this sounds like a dumb question