Those who don’t have a baby carrier typically carry kids on their hips. As parents, we put our kids on our hips countless times per day, and it’s...exhausting. When grandma is in charge, she'll be doing the same. Think about how exhausting it must be for her.
The fact is, little ones love to be held and snuggled up to you. They like to see the world up high like you do. But carrying a baby on your hip can lead to back and shoulder problems as discussed here and here.