F5 Deployment modes: OneArm/TwoArm of any other modes available

One arm deployment simply means you only have one data network connected to the F5. The servers and the clients reside in, or come to the F5 through that single network.

Two armed or more essentially mean you have more than one data network connected to your F5. In a lot of cases you will have a few. You may have a classic external/internal network and then a DMZ network, an internet facing network etc. The sky is really the limit.

The physical connections however can be vastly different to actual data networks being used since a single connection can carry multiple VLAN's and this is quite common. In addition to all of this is the separate management network which is connected to the management port on your F5.

In terms of preference, if you need to use more than one network that is when you would use multiple armed configuration on the F5. Same again if for security reasons you need to use separate physical interfaces.