There are many legal applications for cookies. For example, many shopping stores use cookies to track your visit and remember, what you selected for buying (the "cart"). These stores just won't work, if you don't enable cookies. Another site might remember your color preference. Yet another site might log you in automatically.
On the other hand, many sites use cookies to track you around the web (on many partner websites and for months) and collect data about your "digital identity".
This allows that all websites work as before, just that they cannot recognize you when you revisit them the other day (assuming you closed the browser overnight :-) ). No website can create an extensive personal profile for you and sell your personal preferences (at least not using cookies - if you reveal your identity yourself, that's up to you).
On the other hand, for some selected sites, e.g. your webmail provider, it is desired that they recognize you. For most of these sites, you create a user account anyway and you have to log in. Beonex Communicator can remember your passwords in web forms (a dialog box will appear after you entered the password and clicked OK/Submit) and automatically fill them out for you the next time you visit that page. This means that logging in to a site is as easy as pressing the OK/Submit button of the form.
In order to protect your privacy, session cookies are enabled by default in Beonex Communicator.
If you want to disable this feature, go to Edit|Preferences|Privacy and Security|Cookies and uncheck Limit maximum lifetime of cookies.
There is a workaround:
Tools|Cookie Manager|Manage Stored Cookies)
to remove all unwanted cookies.
If in doubt, just delete them.