Certainly a deck designed under budget constraints, Mono-Green Infect is not without its upsides. The mono-colored manabase means that it does very little damage to itself, making it tougher for the red decks to beat you and leaving you less vulnerable to losing to a Snapcaster Mage + Lightning Bolt deck. You get another turn or two when you're racing and can be a bit more patient when going for it knowing that you aren't under the gun to act.

Being a single color, you also get to play a full four copies Cathedral of War. I'm a big fan of lands that do more than just tap for mana, and without needing to hit additional colors on time, you're rewarded with the ability to play lands with other abilities. With a handful of protection and pump spells, it's nice to start the ensuing battle with exalted triggers on the stack, forcing their hand if they have damage-based removal like Electrolyze or Lightning Bolt.

Mono-Green Infect is a good place to start if you can't afford or don't have access to fetchlands, Noble Hierarchs, or shocklands as the entire deck costs something like 20% of what the other versions cost. Once you have the chance to acquire the more expensive cards, the next step I recommend for Mono-Green is to get ahold of some Noble Hierarchs to fit them in, likely replacing the Giant Growths or Groundswells, as they tend to be a bit weaker without access to fetchlands.