I did plan the layout of my garden, but not where the plants go.
I am gardening on a wing and a prayer (and lots of scavenging) and can't predict what I'll be able to buy!
I have a list of wants and a general "direction to go" with my perennials, but I wait until the plant is in hand and plunk it where I think it will be happy. And if necessary, or sometimes just for looks, I move it somewhere else later.
It's about the process for me, not so much about making it look perfect.