The Best of Both Worlds (1) - S3-E26
Question: I can't tell if this was a mistake or if there's an explanation. When the Borg are on the Enterprise's bridge, the first two are covered in the green light indicating they're being transported back to the Borg ship, but the 3rd one (the one successfully shot by Worf) has no lights, he just fades away. Why?
Answer: Its possible that the Borg use a special transporter for living beings (which is the one with the green glow) and a different one for non-living things (which might not have a green glow). In Star Trek the federation uses a different type of transporter when moving bulk cargo than it does when moving people.
The Best of Both Worlds (1) - S3-E26
Question: Why did the Borg dispatch only one ship to sector 001 in their attempt to assimilate humanity? Why not three or maybe even four or five?
Chosen answer: One Borg ship is usually enough. You notice, they were only able to destroy it because their assimilation of Picard ended up giving his crew a unique 'backdoor' into their system. No one had ever tried to retrieve an assimilated crewman before, because it is usually such a futile effort. So if the Borg feel that one ship is enough, they will send one ship. They are big on efficiency. Sending more ships diverts ships away from other potential targets and missions.
Answer: The Borg use technology to cause the dead to disintegrate, presumably as a security measure to prevent their technology from being captured.
But in s05e23, "I, Borg", Riker says "the Borg collect their dead" when they encounter the injured Borg. Worf says to kill it and leave no evidence they were there so that when the Borg return to collect the dead member. Plus, there were 4 dead Borg and none of them disintegrated.
Bishop73
I believe "collect" refers to the disintegration. We see other Borg remove specific pieces of technology from the dead borg, which causes it to disappear.