The BeagleBone Black has a standard 2 GB built-in flash memory , but that can sometime be pretty close depending on the installed operating system and installed programs .
Moreover, it is quite useful to have certain applications, such as a php- based CMS to run with MySQL database on faster memory such as USB flash or an external USB hard drive .
If your Raspberry or Beaglebone is attached to your network and is doing some Jobs for you, it is important that it is always accessible with the same IP-Address.
In most cases the Network-Router, which is the DHCP-Server as well, will try to give every Computer connected to your Network always the same dynamic IP-Address, but this is not for sure.
By default the Raspberry / Beaglebone is set up to search for a DHCP-Server and to receive a dynamic IP-Address, but it is also possible to give your machine a static IP-Address.