Do I need a sheet of polystyrene under my fish tank?

[Kelly]

I bought one of those fish cabinet stands and matching hood off ebay. Then my uncle gave me his tank that fits the cabinet.

He told me I need a polystyrene sheet under my fish tank. Why is this?

 

[danny boy]

To prevent the glass from cracking and to retain heat

 

[Lestat]

it helps prevent the glass from cracking under the weight