There are lockers in the lounge shower/restrooms. They're only meant to be used while you're showering/changing, is the thing. Not to store your stuff longer than an hour. There is a sign up that they monitor and remove anything left longer than that. And yes, once you leave the lounge, you don't go back in. There isn't nearly enough space/storage for all the early arrivals and late departures to keep their stuff there all day. It's not a big place. Think of it like a small spa shower/restroom situation.
Some people were napping on the furniture/floor in the "living room" sort of space outside of the shower/restrooms. They all had a bunch of stuff with them, although I couldn't figure out why anyone planned to use the space that way. Maybe they were just tired and didn't want to check stuff with the valet? But they did have to stay with their stuff b/c there wasn't a storage space in that area.
We didn't do early arrival, but did do late check-out. We left everything possible with the valet. DH and I each had a small bag that had what we'd need for the day - change of clothes for us and the kids (i had mine and DD's, he had his and DS's b/c the lockers are in the separate spaces for men/women), money/credit card (this shouldn't be necessary for early arrival b/c you should have a room card with charging privileges even without a room yet), sunscreen/hairbrushes. Nothing worth stealing. I used my water wallet thing for my phone, etc. The kids ipads were buried in the luggage with the valet. However, the front desk does also have safes you can use! We had to do that one day when the room safe battery died and didn't work - store wallets and stuff there while engineering fixed the room safe.