Did we have to enable LACP for Trunk?
Is it a must and what benefit?
using LACP is not mandatory. But it helps to detect connectivity failures very fast.
In "short active" mode it will send LACP "hello" packets, which will be reflected by the peer (if it has LACP enabled as well).
Due to the reflection the probing works bi-directional.
I´m using trunks for both link high-availability and scalability.
Since TMOS v10 the so called HA-groups are implemented which can use a trunk´s availability to trigger a sub-second failover. For this type of setup LACP is mandatory.
Interoperability is not an issue with most major switch vendors as far as I can say.
To add: If you are configuring lacp passive on the F5, make sure the other side is active and not passive. There wont be any heartbeats sent out otherwise.
Having LACP also means that mis-configurations where the link is up, but not in the channel at one end will be detected.
It can be very hard to diagnose strange cabling issues without LACP... Especially if it's several different teams (BigIP, Networks, Cabling).