cookies are safe to delete. without repeating details of ome of the great answers you've already got. . .
visit diskcleaner.nl, download and run at least monthly (more often depending on your browsing habits). it will remove a great many unneeded file types from your system with just a few clicks.

A cookie is a simple text file. They have no capability other then to maintain minimal information regarding authentication and site related information. The dangers of cookies are somewhat of an urban legend and not in the slightest bit accurate.

Yes.. it does no harm to delete them. But it also doesn't really do any good to delete them either.

If you visit Ebay.. Ebay looks for Ebay cookies. If you visit Google.. it does the same for Google cookies. Ebay can't read the Google one and vice versa. In modern computers, this action is but a blip that takes minimal resources. So the performance gain if there is any, will be unnoticeable to you.