More USB 3.0 ports allow you to connect more devices to your computer that support USB 3.0. USB 3.0 is an improved version of USB 2.0 which offers faster transfer rates.
Flash-based storage devices such as SSDs have no mechanical components. Due to this they are typically faster, run silently, and are more shock resistant than traditional HDDs.
RJ-45 ports are used for LAN (Local Area Network) connections. With more ports you can achieve increased bandwidth across a LAN, or connect to multiple networks. It also has the added benefit of not losing connection to the network if one fails.
You can detach the keyboard of your device and use the screen as a tablet. Detaching the keyboard makes the device lighter and gives you the possibility to switch easily between laptop-mode and tablet-mode.