13.8.3 Use Designer Blocks When

• The design is congested (uses 90% of the resources on a given die).
• You have difficulty meeting timing by doing the design in its entirety. Blocks enable you to compartmentalize the design and optimize sections before you optimize the entire design.
• You want to re-use some elements of your design.
• You want to use the identical elements multiple times in a single design.

You cannot use Designer Blocks with all families, they are family and die specific; if your Designer Block has I/Os it is also package specific.