It's good to get various opinions. People can decide what they are comfortable with. Even with shims, you still need to do it right. One aspect of the discussion is the tank bottom.
Having a floating bottom tank (glass walls not sitting on the bottom plate) makes it much harder for the bottom to crack. The tank weight is taken directly by the vertical walls sideways - edgeways (which is how glass is stored). So a 60cm high tank becomes a 60cm thick piece of glass which is incredibly strong in that direction. The bottom "floats" and flexes accordingly on polystyrene. For very long tanks (12 foot + ) split bottoms are recommended. I've never had a bottom crack but I've had silicon seams fail.
My first fish room was built on a shoestring budget so I deliberately overhung 150 tanks end side out by 75mm off the stand. Just dangled out in the air but they were only 45cm high. This allowed me to place my horizontal drainage pipe fittings directly onto the tank bottom - saving me the cost of extra fittings and gaining some vertical height tank clearance. Even a $3 saving per tank rapidly accumulates when you get lots of tanks.
Having a floating bottom tank (glass walls not sitting on the bottom plate) makes it much harder for the bottom to crack. The tank weight is taken directly by the vertical walls sideways - edgeways (which is how glass is stored). So a 60cm high tank becomes a 60cm thick piece of glass which is incredibly strong in that direction. The bottom "floats" and flexes accordingly on polystyrene. For very long tanks (12 foot + ) split bottoms are recommended. I've never had a bottom crack but I've had silicon seams fail.
My first fish room was built on a shoestring budget so I deliberately overhung 150 tanks end side out by 75mm off the stand. Just dangled out in the air but they were only 45cm high. This allowed me to place my horizontal drainage pipe fittings directly onto the tank bottom - saving me the cost of extra fittings and gaining some vertical height tank clearance. Even a $3 saving per tank rapidly accumulates when you get lots of tanks.