High Affinity and Low affinity in Cognos

[cognos05]

What does this exactly mean and what value should I set for Report service .

I understand high affinity - does certain task like page down and page up and keeps track of history cursor and fast when used for this purposes .
Low affinity- for general report execution like html or pdf .

What values should I set if most of my users just view analysis studio reports .

Should i set it to 4 -low affinity and 1 as high affinity - what does this do .

I really appreciate your suggestions

Thanks,