I'm assuming you mean cut-to-length plate from coils that has been flattened.
How you know if it's okay is past experience using that product.
I've known of fabricators that would use it for roofs and bottoms and not for shells, and others that would use it for shells but not for roofs or bottoms.
The issues are flatness/waviness in the product as received, and possible increased distortion when welding due to residual stresses.
If the de-coiled steel has been processed with a temper pass it should be OK for any portion of the tank. The issue is the residual stresses from de-coiling and flattening causing warping when these plates are welded.
Coiled steel is typically thinner gauge metal than plate steel. One problem is that coiled material is more difficult to handle and limited by the width of the coil.
