Melissa,
I think it depends on the child. If she has allergies or something, then you may need to do it for the first year or so...
I never used it...after all, he was laying his face/arms/legs all over my regularly laundered clothes anyway...so what was the point?
You might try to wash a tshirt or something in regular detergent and see if she can wear it without a rash or something…I don’t know how you would tell.
I did a quick search and found this site:
Caring For Your Baby
It says
All new clothes, blankets and linens should be washed before they are used for the first time. You should use mild detergent for the first year. Clothes, and especially diapers, should be double rinsed so that your baby's delicate skin will not be irritated.
So there we go!