Why get checked?

Julie
I'm 39 weeks and my doctor wants to check if I'm dilated at my next appointment (this Friday). 
What is the medical reason to check? I don't understand, it seems like being dilated/effaced is not the greatest indicator of when the baby is actually coming. So many women on here say they weren't dilated at all then had the baby 24 hours later, or were dilated to 3cm for over three weeks.
I just feel like getting checked would make me more impatient, won't give a good indicator of when the baby will come, and I don't see any medical reason to check.
Is there something I am missing?