What is the use of incremental aggregation? Explain me in brief with an example.

1) its a session option. when the informatica server performs cremental aggr. it passes new source data through the mapping and   uses historical chache data to perform new aggregation caluculations     incrementaly. for performance we will use it.

2) Incremental aggregation is in session properties i have 500 records    in my source and again i got 300 records if u r not using incremental aggregation what are calculation r using on 500 records  again that calculation will be done on 500+ 300 records if u r using  incremental aggregation calculation will be done one only what are  new records (300) that will be calculated dur to this one   performance will increasing.