I really like it like emergency AOE. When you feel overwhelmed by numbers just place it and activate Also blocking doors is funny. Or using it as a kind of decoy: especially one time I did it great when I didn't have enough AP do destroy goliath a placed it in front of him and next round killed him. Or as a barrier in front of turrents in few places where static defence was an option. Otherwise, if no good use is available just put it behind you and kill some of your pursuers.
Definitely great as a tactic to slow down and kill pursuers havnor
Slowing down Goliaths is also a great move -- he can waste his attacks on the mine, and if you get lucky the mine will keep him busy an extra turn before blowing up. Help the mine out a bit by shooting him lol.
I find them most useful when defending a tact point. I'm limited in the number of fixed turrets I can have, so I drop a land mine next to any known spawn points . The spawned xeno will attack the mine first, and give me time to rush a templar over to solve the problem.
I use both turrets on overwatch and land mine as "speed bumps" to buy my templars enough time either to rush over and deal with the problem or to escape. While I haven't used it this way yet, I might also consider using the talent when having to traverse a large map with an engineer in tow. Leave a present behind me so that pursuing xenos will stop to address the mine rather than simply charging after us.
For both of these occurrences the actual destructive power of the mine is unimportant. What is important is their ability to force the xeno to slow down and deal with them, potentially buying me a turn or two.