I've never understood why the Borg "ignore" those that are not a threat to them when just a minute ago, that same person was being attacked by them or attacking them.
A good example would be the First Contact film where Picard and crew are being attacked or ignored at different times.
Why would the Borg not reach out and zap them when they aren't "a threat"? Doesn't make much sense.
Is this another one of those lazy writer's techniques to heighten suspense? you know, like when the shields can at different times allow for transport but other times because the shields are "up" transport can not be used?