I've had extension table on most of my machines and for a while I thought they were brill, but, I do have to ask myself if they really did help in any way.
Most things I make, bags, pouches, wallets etc all fit perfectly well on the machines standard bed. But then again, so have my shirts and jeans and shorts etc. Fabric just naturally drapes over the sides of the machine.
I suppose it's up to each person individually whether they benefit from the extension or not.