Tall deck blocks allow for longer rod to stroke ratios on standard stroke engines, or they allow an engine to be stroked without getting too small of a rod to stroke ratio. For a standard stroke though, you're better off using a long rod and a shorter crown height on the piston in a standard height block. Tall deck blocks weigh more and having long rods with long pistons adds a lot to reciprocating weight which detracts from power, efficiency, and RPM capabilities.