What is RIP software for printers?

I see that Rip software for the Epson 4800 printer costs 500$, what does it do? Is it needed?
Thanks,
Mark.

from http://www.inkjetart.com/news/archive/IJN_03-17-04.html

RIP is an acronym for "Raster Image Process". RIP software's main function is to convert your files to a raster or bitmap file that the printer can use. Most photographers and other artists are using Photoshop, which typically edits files that are already in a raster format (i.e. ".psd" or ".tif"). All of the Epson Stylus Pro wide-format printers come with print driver software that will allow you to print directly from raster files. You only need RIP software if you regularly print from vector (i.e. CAD files) and documents that include EPS (Encapsulated PostScript) files (i.e. Quark and Illustrator files). And if you only occasionally need to print these type of documents, you can often convert them to a PDF and still avoid the need for RIP software.

Of course, there are other reasons to buy a good RIP program, i.e. for the "nesting" features (allowing quick and easy multiple print size layouts for better media usage and less waste) and the ability to make larger prints (the Epson printer driver has a maximum printable length of about 92"). Most RIP software can cost between $1,000 and $3,000; and many artists, who do their own printing, find they rarely need these features, or they'd rather spend their money more effectively on color management software and hardware.

lol, thanks for the explanation too. I manage three RIP servers at work and wasn't too sure myself what they did.

Thanks a bunch Paul, good explanation. I did not think I needed it, but now I know I dont!
Mark.