Today, I played on Niveus as alien. Humans tried to quickly move to the long room on stage 1. It gave us great opportunity for feeding we used. We couldn't stop them from setting up enough turrets in the long room but we got enough evo points to own their old powered down base. They still had armory, medistation and telenodes there, real feeding paradise. Humans had no chance to recapture the base or decontruct the buildings. The mistake some aliens did was destroying the buildings for them. Without alien help, humans couldn't afford even building a telenode in safety.
Do not destroy abandoned human buildings (except powered turrets, teslas and defence computer you can't power down). If you can power them down, do it. Camp them instead and feed on humans trying to salvage them. If humans leave enough buildings behind you can camp, it can completely cripple them.
Edit: In sudden death, always attack what will hurt most. That means overmind and eggs for aliens and armory and telenodes for humans.
If you have other base crippling tactics, post them here.