Storage and Decorative Blocks have different uses in Simple Ores.
The basic Storage Block is made by filling a crafting table with nine ingot / gems of a material. All five materials (Copper, Tin, Mythril, Adamantium, and Onyx) have a storge block. The most common use for these is to store large amounts of ingots in a small space. As nine stacks of ingots canbe reduced to a single stack of storage blocks, a single chest can hold a large amount of ore. There is no material lost in converting between ingots and storage blocks.
Storage blocks can also be used as decorative blocks in construction. Rarer materials can actually have a strong blast resistance against creepers and TNT.
Bars are a decorative block which can be made from all five materials. Adamantium and Onyx Bars can withstand creeper blasts, while Copper, Tin, and Mythril Bars have a lower resistance. Also, bars have the advantage of being transparent.