I can't find a single use for them. At all.

Put them in peoples pants and run

Its a good tactical choice in many different situations. Its not really complicated, just booby trap the [censored] out of everything.

Find a small, confined space with enemies nearby. Lay a few mines down and then shoot them with whatever pea shooter you have and watch the fireworks. Or what gnrfan said.

Place them on the ground,hostiles get near and they go boom,pretty simple.

The most use you get out of them will be against packs of fast and tough melee enemies that run directly at you such as deathclaws,nightstalkers,tunnelers and super mutants.

Frag Mines are good for crippling the legs of your enemies. Especially useful if you can get Deathclaws to run into them.

Their practicalness is fairly limited. The time you lay a mine, you could use your main weapon to deal the same amount of leg damage to the enemy. And most enemies don't even need such firepower as mines provide. Deathclaws are the only one I can think of and even they go down quickly if you see them first.

Mines can be quite useful in situations when you know in advance where the enemies will spawn or which way they'll be headed, because you can then boobytrap their approach routes. Most obviously, you can exploit that during the final battles of Ghost Town Gunfight and I Forgot to Remember to Forget, and in the final stages of Dead Money, when every side quest you complete causes Ghost People to spawn in the casino lobby.

Bottlecap mines saved my butt against Deathclaws in Fallout 3. Not so much in NV.

If you have lonesome road theres this truck thing where a deathclaw will span on its roof a good stratagy would be to just tell ed-e wait near a minefield of your own and wait for the big boom!

courier's mile. and you can use them for this thing called 'fun'.

Walk into ceaser's tent....

Stand in the entrance and throw a rocket at him...

Leave the tent ....

walk past a crap load of land mines....

watch as the legion hits every single one on their way ...

You, boone, and ED-E pick of all the crippled savages ...

... And that my friend, is the use for land mines ....

I found them useful with my sniper character, if you are sniping mele enemy′s lay them down for protection in case something goes wrong.

I found them to be awesome in Old World Blues. Lobotomites and Y-17 Harnesses love to follow me into buildings, so I always put a frag about a meter in from any door I go through.

They're also wonderful against Robo-Scorpions. Trick the things into coming at you with their claws, then just toss mines and retreat. Similarly useful against other scorpions, Legate Lanius, and Father Elijah.

-Nukeknockout