When a Release 8 map is compressed, the file size gets reduced. You can see a similar effect by taking a Radian .map and zipping it. A good example is the Wildfires.zip file I've attached, which is 10 KB as a zipfile. Unzip it into a .map and it grows to 1 MB, 100 times bigger. That's a super extreme example, of course, as zipping a Radian .map won't normally make it 100 times smaller.
Release 8 can be set to automatically compress map files because the technology within 8 is not capable of accessing the innards of a .map all that much faster than a good unzip algorithm can decompress it, so it is not a bad tradeoff. But try to open a very large image in 8 and you're going to think right away that "heck, rather have a way bigger file if that makes it go faster."
For an extreme example of that effect, watch the video at https://www.youtube.com/watch?v=Gvib5LqqE2o
There is simply no way Release 8 (or, for that matter, most other applications) could handle even 20 GB worth of images as fast as that video works with 110 GB worth of images. With Release 8 I get the feeling each step (pan, zoom...) would be the sort of thing that you would launch at the end of the day so it could cook overnight. With Radian it is instant. You do pay for that instant speed with larger file sizes, but, heck, those are cheap.
But you get other benefits with those as well. With Release 8 if you make a small change in a big vector file it is really painful to save that file so you don't have to worry about losing the change. With Radian / Future / 9 if you make a small change the save, just like the open, is instantaneous.
Newegg.com sells plenty of 4 TB hard disks for $119 and you can buy 8 TB for around $250. Storage has become very inexpensive, but the cost of your time keeps going up, so if a larger file size makes GIS significantly faster for you, well, that's not a bad trade off.
By the way, in terms of zip drives, it is way cheaper to buy one of the new, slim 1 TB portable external hard disks for around $55 than it is to buy a USB flash memory zip drive.