Ever since I was a kid, up until now that I'm middle-aged, I've always wondered why, in wars or otherwise, they bother digging down mines which explode when humans tramp on/near them. This seems like such an insanely inaccurate, indirect, devilish and, most of all, stupid way of going about things.
The obvious main problem is that not all the mines will be stepped on/explode during the war. Another obvious problem is that your own soldiers, or civilians, will accidentally step on them, during or long after the war.
It just seems stupid to me. If you are going to put them down, at least limit them to a specific place and in front of an important stronghold that you suspect will be attacked, to stop the enemy. Preferably mark it as a mine field very clearly, and make sure to sweep it after the war, or at least leave records of where the they were put down, so that others can do it later.
It seems like a ton of work and risk for very little reward. Those mines aren't free to invent/improve/manufacture/dig down/keep track of/deal with later, either.
Things might be clarified if you think of sea mines. There are command-detonated mines in your own ports, mines laid on enemy coasts, moored mines which might break free, and mines that were drift mines to start with.
The same princles apply to land mines:
In defensive use, mines will slow or block the enemy in just the right place for your weapon fire. Much like a field of concertina wire, except that mines are harder to clear. While the enemy tries to clear the mines, shoot him.
The other defensive use is for dead ground around your defensive positions. If you are on a hilltop, and there is a ravine where an enemy might place mortars, mine the ravine.
Those two sound halfway legitimate to me, provided the forces which emplaces the mines keeps accurate records of the minefields.
- Mines can also be scattered on important roads and crossroads to cover a retreat. That's called FASCAM by the US.
Slightly more iffy, because there can't be any accurate maps. Still, if it is done defensively on your own territory against an invader, it sounds somewhat justified. A big problem is that these systems are unreliable, some have self-destructs which might not work, some might be scattered off course.
- Offensively, mines can be placed in random places in the countryside, without any recognizable fields. That denies the use of that countryside to the population.
This bullet point is somewhere between immoral or a war crime, if you ask me.
I think one important point you didn't consider is that mines work long-term, without binding personnel. You spread them across as many access areas as you like, and walk away, and you are protected from attacks through there.
Any other such protection would bind personnel near the places, for an attack that might never happen.
So they are an indirect but significant 'increase' of available soldier count. Having double the soldiers obviously is a major advantage, for the cost of some cheap mines that do their work.