It is fairly easy to reuse the placement of I/Os, Global Clock Resources, Block RAM macros, and DSP macros. Re-using this placement helps to reduce the variability in results from one netlist revision to the next. These primitives generally have stable names. The placement is usually easy to maintain.
Tip: Do not reuse the placement of general slice logic. Do not reuse the placement for sections of the design that are likely to change.