Snake gaiters protect your legs from venomous attacks.
Snow gaiters prevent water and wind intruding into your footwear and making you cold.
Backpacking gaiters keep everything out of your footwear. If you wear trail runners when /out/, lightweight breathable gaiters are necessary to keep out scree, brambles, thorns, sticks and ticks, fireants, and light rain while allowing sweat to evaporate.
No need for them in the summer on a paved, grass or tight dirt trail. But gaiters are part of a good system under rugged conditions.
They just work, unlike goretex lined boots, which are stupid, although goretex socks can make sense.
