it depends on how often you are doing the searches.
I have one (vendor-written) application that occasionally decides to do a half million queries over 36 hours. It does a separate bind and unbind for each, and as the LDAP system administrator, I really wish it would bind once then do the
I also have applications that make connections and do not use them for hours on end. They tie up resources, and the dead-connection monitor on our load balancer and on the LDAP server tend to kill the connections when not in use that long.
If it's going less often than between every 15-60s, then I'd set up and tear down for every batch of searches...