Mega Memory Cards are what deemed by the industry memory Cards exceeding 512 Megabytes in space capacity, and with prices of memory becoming ever so cheap as how prices of cameras too. 10 years ago, a 32 Megabytes card is deem the biggest about costing over $700 with proprietary usage with Sony or Fuji XD cards.
Let's start with the CON first.
Memory cards have many formats. Knowns commonly as Compact Format CF, eXtended Definition XD by Fuji, Memory Stick by Sony and Secure Data or SD . Most common in cameras nowadays are CF or SD cards as they are very cheap, too good to be true. Some are offered at $200 for a 8 Gigabyte Card but as you might think, it may be too good to be true.
Memory cards have speeds too, just as how RAM are. Remember the days that ram are clocked at 100,90,80,70,60 milliseconds? It's the same aspect to how one would rate a CD ROM Drive at how many X's it has for the read / write capacity. Memory cards basically run at a lowest speed of about 1X of the CDROM Format, which is 150kilobits per second compared to the professional end of 8 Gigabyte Memory card for about $1100 which is called Extreme 4 format, as it clocks about 15-30 Megabytes a second compared to the 8-10 Megabits per second for a Extreme 3 costing about $900 instead. In contrast, a cheapo memory card used for the mobile phone / cellphone or PDA can take these cheap memory cards as their data bus are about 100megahertz (100Mhz) a second, which means it's fine for low end usage, just as how you compare speed of USB1.1 and USB2.0 which limits to 1.3Mbps and 480Mbps respectively.
When you have a good and quick memory card, with loads of space, you tend to overdo yourself, snapping as much pictures as possible,but forgetting that after you upload then, you have to do some sort of editing like modifications to the contrast, hue, pitch or what we call them photoshopping or Picasa-ing for the novice entry level.
My wife is a guilty of that, and after a day of photo shoots, she will be cussing and swearing about her load of photos to modify, and on the standard MEDIUM SIZED 1500 x 2500 pixels image, a 4 GB card can take about 3200 photos, and with a DSLR camera, you get to empty your battery pack first before you run out of memory. Trust me on that one.
Now for the PRO.
As I said, space and Speed is the essence. I use a Canon EOS 400D with shutter shoot of 3 frames a second and a trigger hold of 30 seconds, meaning I can snap at a go about 90 photos without the need to stop and look. Just as an automatic rifle would do. This is a 10.1 Megapixel camera with 17-200mm telephoto lens with Wide Angle added to it. So the base unit cost me et. al about $5000! The lens cost me more than the camera itself!
So, with 90 photos to load from the buffer to the card, it means the cache memory in the camera (64MB I think) has to be able to access the memory card quickly, and only Extreme 3 versions are capable to do so. And SD cards don't have this speeds yet, so thus why professionals and paparazzi all uses quick memory cards.
Another issue is when you already loaded up, you can just offload them to your computer just as quick, compared to a slower card. With a 4GB Card like I am using, it's as if unloading the whole DVD to the PC in 3 minutes or less compared to the Cheapo Brands taking as long as 15 minutes. It's the databus that is capable of loading quickly, but also, that your hard drive in the PC must be equally quick.
One great advantage when you have mega memory cards is that you tend not to run out of space. It's like you have a good photo opportunity like some celebrity in town and you so happen to be there, of course you want to be THE GUY to be able to take that shot.
There are many Pro than con in the usage of mega memory cards for photography, but I too use a huge memory card , the Micro SD for my Motorola Cellphone, which is used for my MP3 player. Cool huh? Oh yeah, if you use good ones, you don't need them DVDRAM discs for your Camcorder, just the memory stick will do just fine. It's either that or the Hard Disc Drive format.
But I will surely invest in an Extreme 4 (or Extreme 3 at the very least) for my usage.