I agree I hate that people get up early and place personal items on a lounge chair so it can sit empty till they decide to use it. Not that I am proud of it but many years ago at Las Ventanas I got up early to use the pool and watched a guest come down and dump their stuff on a chair. It happened to be windy so after my swim I walked by and dumped it in the pool.
At the Setai in Miami Beach I was very happy sitting front row one morning looking at the sea. About 11 am the beach attendants came and set up a new row for a couple right in front of me, umbrella and all blocking the view.
My visit to Amanpuri it was very clear to me that the front row was reserved by the beach attendants for guest already at the resort. You could move into those seats once the guest checked out.
So yes I hate it!