Bots are highly maneuverable legged units designed to outmaneuver their slower tank based counterparts. Bots are as a rule less heavily armoured than Tanks of the same Tech level, but with effective micromanagement can bring down the tanks with minimal trouble. The Cybran Hoplite and UEF Mongoose are examples of units which excel when managed well. Tech 3 ground units are generally Bots, as well as some Tech 1 units. Bots are fast, and agile units great for scouting and raids. Heavier bots like the Percival and Brick are slower than most other bots but they are much more powerful.
The Tech 1 light assault bots, the UEF Mech Marine, the Cybran Hunter, and the Aeon Flare, have a unique ability: They are the only Bots, or land units in general, able to fire their weapons while on a transport. Players have exploited this technique to create a makeshift air-to-ground aircraft, dubbed the "Ghetto Gunship". Although LABs are weak, and as such don't find much use on the battlefield, they can severely damage an army when fully loaded into a transport and survive to do enough damage, as opposed to lasting just briefly in a firefight. The UEF have a significant advantage in this, as their T2 Gunship, the Stinger, has a single transport hook. Since that one hook wouldn't have much use in transporting, as you would probably need that gunship for its combat role, why not give it an extra 21 DPS?
The UEF also have a Heavy Air Transport, which convientely has shields and Air-to-Ground weapons to begin with, so your LABs will be protected.