Collect stats doubt - forum topic by tigerjgd

Hello all,
 
In which case we go for multi column stats .
when we have a clause where table1.id=table2.id1 and table1.flag=table2.flag1 -- here
we can seperately collect stats on flag and id. There is no need for multi column stats.
Could somebody explain for which data demographoics teradata cannot predict the column details and hence we go for multicolumn stats??
Thanks
Aravind