how performance increases for free characteristics

Hi experts.

1. in reporting ,if we put chars under free characteristics. whether it will increases query performance or not. if yes. how it increasing.

2. when the query executing first time it will fetches data from data base tables. if it executes second time it fetches from OLAP Cache. suppose again we load new data to cube. now we executing the same report , wether it fetches new records from database tables or olap cache.

3 what transaction for how much time taking to execute the report.

4. how can we see the ratio between dimension tables & fact tables.

thanx in advance