The biggest advantage of star schema groupings is that they make it easier for report authors to build valid reports by avoiding double-counting and misleading associations between dimension data occurrences. In addition, performance can be faster when there are fewer tables to join. Star schema groupings also reduce the risk of users creating huge queries by mistake, and they are easier to manage, maintain, and enhance.
RE: Can anybody tell me about star schema grouping
Star Schema Groping Is a process of creating shortcut for you selected query subject,dimession masure and relationship  for easelly understanding between relation between your regural dimession and masure dimession .and when ever you use conform dimession at that time you  make shortcut conform dimession for each namespace .Star Schema Groping is also help full to reducing ambigous join.for that purpose we use star schema grouping.
Star schema grouping is only help full when ever you working more than one data mart(when ever you creating more then one namespace at that time star schema grouping use full)
For Single data mart no need to create star schema grouping.
