The use of minefields is critical in defense as it unseen (unlike barbed wire that can give you a good idea of an enemies defensive layout) but has almost similar effects: you can't move through it quickly.
This gives the defender a great deal of leverage in terms of building a foundation that can be almost impassable when done correctly.
For the price of a T-34, a Soviet can purchase 10 AP minefields and completely rampart a whole flank so that NONE SHALL PASS.
The good thing about the mine is that:
1) the enemy cannot see it like wire.
2) once the enemy is in it, chance of panic will rise if pinned and almost always breaks the unit.
3) you can defend a flank quite competently with no more than a platoon or two.
EX:
Normally I would use half squads and a +2 command HQ platoon in a defense like this, with a Battalion or company commander to give all the spread out troops command influence.
The other tactic that is exceptionally good is to mine deep woods (if you have them on your map) where you know the infantry may have to traverse through (such as right in front of your flag). Mines make an unpassable barrier where troops set up defending behind (FT's, Pioneers, etc) can knock the crap out of any advancing troops without much harm coming to them from infantry fire, or outside HE.
The nice thing about flank mining, is that if you do a solid enough job, even if your enemy overloads that flank, you have enough defense and time to shift troops over, as the first wave of the attack will usually break on the minefield, your troops defending it targetted and then the second enemy wave.
Hope this helps!
Cheers!
Leto