If you design your applets to take advantage of multi-session functionality, they can interoperate from different channels and can be selected multiple times in different channels. For example, the card might handle security information on one channel, while data is accessed on a second channel, while the third channel takes care of data encoding operations.
By following this design, it is possible to access information owned by a different applet without having to deselect the currently selected applet that is handling session information. Thus, you avoid losing your session-specific security data, which is usually stored in CLEAR_ON_DESELECT
RAM memory.