Tarp under tent?

Do i need to put a tarp under my tent? My tent kind of has one but thought I might need to put an extra one under or would I be ok cause we're on grass?

Thanks !

I always put one under anyway. That's what I learned in Girl Scouts way back when and never broke the habit. Can't hurt that's for sure

Especially after coachella being there the last 2 weeks,not sure how much grass we will actually have.

Also,
It's supposed to rain in Indio tomorrow, so the ground might be a little damp