I've done this in two places in low level zones, to split spawns that otherwise I couldn't. I don't know if it will work in higher level zones, or if its a well known tactic. Its of limited utility, but its not useless.

With mobs that assist, you can use this to break up larger groups. In the warrens for example, is a room with two kobold pit fighters. These pit fighters are level 14-15. Normally if you get one, you get both. However, if you aggro another kobold, and are fighting it, then you can edge closer and closer to the pit fighters. Eventually the nearest one will break off and come charging up to assist his little buddy. At which point you run like mad back to your kill point and take them both out. That way you are fighting say 1 level 8 and 1 level 15 mob, instead of 2 level 15 mobs.

You can do the same thing hunting heart spiders in Upper Guk. The second room from the bottom is a three spawn. The bottom room is a 2 spawn. Aggro the bottom room, and kill them. Drag out the death of the second one a little to create a nice break. Hang out for respawn. Kill first one. When fighting the second one, edge toward the upper room. At some point, the nearest spider in there will come to assist his pal, leaving the other 2 back in the room. 

This might be a way to split tough guardians, so that you have fewer to deal with at one time. Then again, it might not, since there is a rather large difference between Upper Guk and the outer planes. 

Thanks for saying its very clever - I tripped over it by accident. 

You can use that as an SK as well. In the Feerott, hunting lizards, you'll find some heavy healers. Annoying, and not worth the trouble of killing. Especially when you get more than one at the same time.

So snare the one you want, and run to a spot where you know the pathing. Fear the snared one. Run for the guards with the healer in tow. Let the guards take care of them. Head back, the lizard you want will find you. In Netherbian, just snare, and run for a guard. The guard will engage the unsnared ones, and the snared one will run around the guard to get to you. 

Hopefully, with feign death now, I won't have to do this sort of thing quite as often.