Our concrete guy didn't even ask. He just did it.
For as little as it costs it doesn't seem like over kill to me. We also sealed plastic over the gravel and have a 4" exhaust pipe inserted for radon prevention. Yet again the small cost is worth it.

Drain tile is cheap....I have it on the inside and outside

my builder will do interior, but he said he doesn't see a need for. I am pretty sure I understand it (well, outside anyway) what does interior drain tile collect? water under slab floor? if it matters, we are backfilling with gravel (to help w drainage plane and hydro pressure

I've only used an interior drain tile where there was a special concern about water--as when the excavation for a walkout was continuously filling with water to the level of the exterior tiles.