In many application scenarios, it is necessary to update the program to upgrade the functions or fix the known problems.
A lot of communication protocols can be used for IAP (in application programming).
USB can be used as device and host, and both can be used for IAP.
The USB host IAP can be realized without the assistance of the upper computer and only with a mobile storage device (such as USB flash disk).
The other communication protocols do not have this advantage.
The allocation of the whole chip is shown below.
For more info see the AN034 is here and is for: M3/M4/M33.