Iconize behaves in a confusing manner

Think of whatever has been iconized as being exactly identical to the original data (it is!). The icon is essentially just a representation that fits nicely into the front end without taking up your entire screen. For all intents and purposes, it is the original data. I often use it if I have a large data set (a few thousand rows) that I want to store inside of the notebook rather than re-importing it every time.

If you click the little plus button on both, you should see that the two icons contain different amounts of data.

When using Iconize, Mathematica does not assign the data to a variable, therefore it cannot be overwritten by calling Iconize again, even if the two icons are given the same label. What happens is Mathematica cuts the data out of your Notebook, transforms it into an icon, and then pastes that icon back into your Notebook. Therefore, it is possible to assign an icon to a variable.

Notice the differences in the way I use them below. r2 + 5 returns the icon plus 5, but the icon itself (r3) plus 5 returns the list with 5 added to each element (the same as r1 + 5).

A useful way to use icons is to type:

r4 = Iconize[Range[15], "My Label Here"]

Then select everything after the equals sign, choose "Evaluate in Place" from the Evaluation menu, and then evaluate the entire cell the way you normally would. r4 is now exactly the data that you iconized and can be used in the same way that your data would be. Notice that this is different from if you were to type the above and then simply evaluate the cell.