Long ago, when people were a bit more flexible and in touch with the land, there was a short little rhyme that taught people how to separate sedges from grasses. It is no longer socially acceptable, but goes "Sedges have edges and cut, Rushes rush down with joints in the ground, but Grasses like asses are round and have holes" This taught young and old alike how to differentiate the two; crude and funny, but everybody would remember. Back then the differences were important. Why was this important and is it still important today?
For starters sedges have tough triangular stem. The edges can indeed cut or tear skin, just as paper can, and those cuts can hurt. If one was collecting feed for sick animals, you don't want to feed them a sedge. Not only is it harder to digest, but the edges will make the mouth sore and the animal will be less likely to eat. Proper nutrition is essential for helping an animal recover from illness.
The rushes mentioned were usually located around ponds, stream or marshes and used for weaving and making baskets. A common rush would be "cattails". They look like grasses and sedges, but are different.
Grasses are digestible, circular and smooth; making some nice bedding and easy on the mouth. They are also nutritious. Most grasses are edible and they include oats, corn, and Fescue for livestock, to just name a few. Grasses are also used on lawns, golf courses and playing fields, they are tough, but don't cut. Some popular types for this include Coastal Bermuda, Zoysia, and St. Augustine.
So, while few people cut their own fodder for livestock, it is still important to be able to differentiate between sedges and grasses. On hikes or even walks in the park, many people will pick a blade of "grass" and chew on it. If one gets a sedge, this can be dangerous. Many types of sedges are poisonous, and that can be really bad for a healthy animal much less a sick one. Star Grass, which is a sedge, can increase urinary tract flow, inconvenient for an older person but a young child can die of dehydration. Ironically enough, it is this diuretic effect that makes Star Grass useful. In the old days, it was made into medicinal teas to get rid of water retention and lose weight.
Are there any other reasons why it is important to know the difference between sedges and grasses? Only that all knowledge is valuable, even if it is outdated or seems weird. One never knows what one may need to know!