What is the impact of adding a floating IP to an active HA LTM pair?

I.e. or outbound traffic (outgoing requests for DNS, NTP, whatever) it may be necessary to have a virtual address (floating self IP for SNAT automap). (Perhaps your external firewall is applying the source NAT?)

 

If this is not the case, you can simply save it.

 

Often people try to save routable IP addresses that way.

 

Btw, there is an alternative:

 

Use a transfer network with non-routable IP addresses. The external floating self IP will be used to act as next hop for your firewall to forward traffic to a virtual address space on your BIG-IPs.

 

Indeed your virtual IPs do not need to belong to a locally attached network. Theoretically they can be reached through all attached VLANs, as long as you are not disabling/enabling it specifically in your virtual server settings.