So many guidelines to this question and you should also take into consideration, the size of the quilt. My labels can be on the large size if I do them on my embroidery machine and on these I put my name, date and who it's intended for.
I make address size labels on my ink jet printer that work fine with small quilts and my stuffed animals.
The larger quilts that I sale I hand write my initials and date only on the bottom right hand corner of the quilt in fabric marker.
I usually just verbally share the washing instructions - a gentle cold water wash and low temp dryer or hang dry but I never make a label to state that. As you mentioned, it would certainly weigh it down a lot more if I did.
Good luck in finding what works for you.