The recon infantry regiment is seen in every online game, and is also the cheapest regiment in the game at only $25. Prized for their ability to quickly earn experience for your special ops, recon infantry are easy to micro and can perform a variety of battlefield tasks successfully. Such as:
 

 
Recon infantry are loved for their ability to quickly earn experience for special ops and their easy micro; and are also equally hated for those same reasons. The recon rush is considered by many to be an unskilled noob tactic, and some have suggested it charges experience so fast that it is unfair, and upsets the balance of the game. Love them or hate them, recon are a part of the game that every player must learn to use, and deal with.

Recon are essential for capturing cities in the early game, and are well suited for the task for several reasons.
 
• At only $25 you can deploy alot of them to attempt to capture multiple cities.
 
• It's often a foot-race to get to a city before your opponent, and recon are one of the fastest regiments in the game; due to the trailblazing modifier, which only effects recons and commandos.
 
For details, tips and tricks, regarding Recon and Cities: Axis & Allies Cities

Well they wouldn't be called Recon without some Reconnaissance... Using a spare recon regiment to explore unsupplied areas for potential threats and intel offers benefits throughout the game.
 
"Just drive down that road until you get blown up"
^{George S. Patton (Instructions to reconnaissance troops)}

The concept is simple, and prevalent in most RTS games, take the cheapest unit, make as many as possible, and rush the enemy; hopefully catching them by surprise.
 
You must be swift - time is of the essence if a recon rush is to be successful. The trick to the recon rush is to hit your opponent while they are still building up their eco.
 
You must be silent - the recon rush is easily countered if your enemies know it's coming. Don't show your hand too early, and take the road less traveled to the target, avoiding enemy cities, supply, and regiments when possible.
 
Can you be deadly? - that's often a matter of perspective... From a combat perspective, against a reasonably skilled player, about the best you can hope for from the recon rush is to kill a few regiments, and if your lucky maybe destroy an HQ or two. In a 1v1 that would be a death blow, but in 4v4 play would probably only be a minor setback for the enemy. However, the goals of the recon rush are usually not the outright defeat your enemies. Often recon are used to simply charge experience for a special-op bomb, or to keep the enemy occupied while you build your economy (Fabian Strategy).
 
One condition that must always be met with the recon rush is, while fighting you must keep them within your zone of supply at all times! Recon rout quickly, but will also recover and heal quickly if kept in supply.

Experience for your special ops in A&A is earned in variety of ways, the main way being through combat. This combat experience is earned on the regimental level, without regard for how many units are in the regiment.
 
Recon are the cheapest way to get to your regiment cap of 20, and in turn offer the fastest way to charge your experience. While 20 SaS or Mortars will generate more experience than 20 recon, this comes from higher combat effectiveness; likely receiving more bonuses for killing and destroying enemy targets than recon would. However, it will take you much longer to deploy 20 SaS or Mortar, hence the popularity of recon spam to charge powerful special ops such as the carpet bomb, nuke, etc...
 
For more on special ops see: Special Ops - Axis & Allies RTS

The fabian strategy is a cautious strategy of delay, and avoidance of large scale direct engagements. Usually used to "buy time" to build economic and military strength, the fabian strategy is a favorite of the eco whores of A&A. By taking a limited number of troops, and entrenching them in good defensive terrain, you can concentrate most of your resources toward booming your economy.
 
For more see: Military Tactics: Fabian Strategy

Once you reach the mid-to-late game, recon have little value fighting on their own; but that doesn't mean you have to kill them off quite yet. Due to the regiment cap of 20, eventually you will need those "roster spots" for stronger regiments than recon; but until then there is still some they can contribute.
 
Mix and Match - trying mixing some recon with your at-mech or armor, not because they will deal out much damage, but it gives your enemies less time to heal. It also gives enemy regiments something else to shoot at, as you would much rather they are wasting attacks on your recon; than attacking your mech or armor. At the very least it will require your opponent to do extra micro to avoid attacking the recon.
 
On Point - send some recon out in front of your arty tanks, as it will extend their view of the battlefield and allow them to bombard targets that would otherwise be hidden by the fog of war.
 

Recons deploy fast and are the only regiment that come out from tents with full health, so if your base ever gets ambushed, recon spams will often buy you some time to coordinate a defense.
 
Recon infantry won't be enough to defend your base on their own, so make sure to get some more capable forces back home asap.

Get a basic idea of which upgrades effect which infantry units, and how to apply those upgrades in online play. Included is a suggested upgrade order to help newer players understand which upgrades are the most benefitial to their cause. See: Upgrading Your Infantry/Airborne