Assuming you are speaking of PBA, this option is for reporting. Usually the reports are generated on graph based analysis and the numbers are pessimistic as the worst case transitions/delays are assumed.
In path based analysis, you trace the actual path and transitions resulting is accurate numbers but with a run time impact. Look up in Solvnet, there are very good materials regarding this.
Both are reporting options and use different path tracing algorithms.
GBA: This is fast, slightly pessimistic and uses worst values across each cell in the path.
PBA: More accurate, time consuming and uses exact path tracing and exact propagation values.
GBA is used for most of the design cycle and PBA is used towards the end close to tapeout. Create a Solvnet account, should take few minutes, I dont think they have PDF files which I can share.