When a user comes to your site via an affiliate link, a cookie will be set in the users web browser. Normally, with a setting of zero (0), the affiliation only lasts as long as the user keeps their web browser open. That is, if they don't purchase something and instead close their browser, the affiliation ends.
Setting this to a value other than zero, will allow the cookie to stay around for that many days. This would give credit to the affiliate if a user arrived at your site via an affiliate link, closed their browser, but came back later to your site by typing in the URL (rather than visiting through an affiliate link) and purchased something (within the specified number of days).
In the affiliate industry a 15-30 day cookie duration is pretty standard. The longer the duration, the more attractive your program is to affiliates.
The Affiliate Manager sends emails to new affiliates notifying them of their approval status. By default, WordPress sends these messages as:
WordPress <wordpress@[sitename].com>
You may choose to override the name & address with something more suitable. These addresses will only affect emails going to affiliates regarding their approval status.
Enabling impressions will cause creative views to be tracked, even if they are not clicked on. This is done by adding pixel tracking code to affiliate links, which records the affiliate and which creative was viewed. This can be useful for determining creative click through rates, but can add a significant burden to the server as far as additional requests and data storage (depending on the frequency of creative views), which in turn may slow down page loads where a creative is shown.