Are trays really required in canister filters

I have two jbl 1501e canister filters with me and they each have multiple trays. Sometimes while cleaning the media in spite of carefully putting the media back on each tray the closing of the canister gets hard. Can one do away with all the trays and just fill media to the top of canister filter keeping a pad at the bottom and top only and close the canister and start running it.

The trays certainly make it easier to hold the media if that's what your asking. The manufacturers manual will tell you how and where to put your filter sponges for best results.