Infiltration can be a part of a reconnaissance or an advance-assault tactic and can be supremely powerful when used properly. Infiltration entails sneaking amongst your enemy to observe their movements with a supreme clarity or break their back from the last-line of defense outwards allowing a second attack-group to enter.
It can even be used in conjunction with sabotage - ruining your enemy's ability to coordinate with a carefully planted charge or even having a man on the inside working for you who'll perform this role very quietly.
Infiltration grants you superior movement within enemy forces or within a range superior to that of your enemy's enemy. Infiltration can be as simple as planting a charge or device to break enemy communications to sniping a VIP due for transport.
Ironically, infiltration usually involves getting out of your armor so it shouldn't really be considered armor combat. Normally you will switch uniforms or switch to civilian equipment and hide your armor - often by burying it or sinking it to the bottom of a lake.
Should the armor be needed, it can be recovered. A good infiltration/ reconnaissance armor will continue to function, filtering comms traffic and providing you an advance warning if your cover has been blown so you can board the armor and make your way to recovery support.
Infiltration is extremely powerful when used properly and is extremely decisive but can be incredibly dangerous.