Talent Pool helps you to divide your candidate database into multiple groups. Grouping could be based on skills, location, job title, experience etc.
For example you want to divide your candidate database on domain like banking & finance, manufacturing, oil & gas, IT etc. you can very well create different talent pool into the system.
Whenever you get any job on oil & gas, you can perform candidate search on the oil & gas talent pool only where only oil & gas related resumes are stored. You can avoid the search in complete candidate database.