Never having done it, if I was to design a backyard and pool, I would stake everything out and create shapes with strings between the stakes. Even the various sections in the pool, the decking, the BBQ area... everything. Then walk around it, sit near it, in it. etc. Chairs and tables, umbrellas, chaise lounges especially, take up way more room than you might think. And not just them, but the space necessary to comfortably navigate around such things...
When I was designing a breakfast bar for my kitchen, I was really concerned about how it would impact the adjacent dining area, the kitchen itself, and especially the clearance between it and the refrigerator, and how more than one person would get into and move around in the kitchen with the new bar in place. So I built the whole thing out of cardboard and lived with it for a while, I think it was for at least a month, maybe two (I wasn't in a hurry!). I changed its size and shape a couple times based on that process. It's now perfect.
I can't imagine planning a pool without doing something to simulate it, including placing tables and chairs (or simulating them, too), to see how everything would feel...