Reddit reviews Battletech 15: Close Quarters (Bk. 15)

This answer comes in two flavors:

Infantry was added to the Battletech rules set as means of expanding the tactical possibilities and increasing the replay value of the game.

Crunch wise, the rules were tacked on and will take hundreds of men to reliably threaten a mech on a game field. In the absence of situational objectives or scenarios, they simply do not function at the level the rulset was intended to play at.

Fluff wise, units of soldiers represent some of the background 'noise' against which the story of stompy robots is told. Books such as Mercenary's Star by William Keith and Close Quarters by Victor Milan, show a much more personal interaction between foot soldiers and mechs, and will answer your question in a very entertaining fashion. But ultimately the focal points of Battletech are the mechs, not the infantry, and the stories generally bear this out.

In modern land warfare, infantry IS the battle, everything else exists to help him do his job: Make the other guy die for his faction..

• Recon vehicles to find enemy.
  
• Artillery to blow up the enemy before he gets there.
  
• Trucks, APCs, and helicopters to carry him to the battle.
  
• AFVs, IFVs, and gunships to carry the weapons into battle that he cant.
  
• Tanks to reduce the strong-points and to kill the vehicles he cant.
  
• Air support to do the same when there are no tanks around that can.
  
• Anti-aircraft systems to shoot down the enemy air support that is trying to same to him.
  
  in reference to your other thread: What part of this ballet do you think a battlemech will dance in?
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  Bonus question time-
  
  In Battletech, a battle armor unit is a better representation* of the threat infantry represents to an armored unit on a battle field.
  
  In reality, the physics of the Battletech universe is incompatible with our own, so without accounting for that, a comparison is essentially meaningless. (It would be bloody cool to have battle armor kicking around in real life though)