I've seen so many LCD shields out there and such and many of them have SD support. My question is, why?
Is it just like, yo you get a bonus SD thing going on here, or do you need to have the images on the SD that you want to display on the LCD first before they can be displayed.
sometimes yes, thats the best way due to the limited resources on chip
4D Systems' displays come with SD slots that have numerous purposes -- storing images, fonts, scripts, and any other data you wish to store on them. They can be used directly by the display (presumedly faster than sending image data via serial), and worked with via the serial interface for data storage.
or do you need to have the images on the SD that you want to display on the LCD first before they can be displayed.
Yes you do. Just think about how much memory is in the arduino and how much you need for a full display of pixels, don't forget if it is colour then you need three bytes per pixel.
Yea, I didn't think about the actual math.
It makes complete sense now.