I haven't found the sliding deck to be an impedance yet and is quite useful especially on Costco or grocery shopping trips where the flexibility to slide the tray out saves my back loading heavier things at the deeper end. Can also recall it helped on a furniture shopping trip where the store employee commented the ability to slide the tray out was a life saver compared to other SUVs that don't have it. Other than that I have a portable fridge sitting on there most of the time and does help with loading/unloading that when necessary.

On a semi related side note, the OEM cargo tray cover in its out of the box form sucks a big one. It doesn't fit quite right and doesn't really stay in place by itself. Had to add some Velcro underneath to help it stay put. It's now a non-issue but you'd figure Toyota would have done something to make it better than it is unmodified.