Currently the only variant of negative/dangerous tiles are the death tiles. They will kill you instantly, no matter how many health you had left.
This is probably one main reason why they aren't used for vanilla maps at regular positions. As example, they are used on ctf5 to kill players that fall down.
I would like to see some less deadly varaint of death tiles: damage tiles. They will damage you slowly (like one point per half a second).
They will add new game technics. You could add...