There doesn't have to be a special reason to be putting '능' at the end of sentences and you're right, it doesn't change the meaning of the sentences but it lightens the conversation you are having. People don't really say it when they speak to others in person but they used to say it a lot on the internet just to sound cute and it does sound cute but there are some serious people who don't take it as cute. I guess that could the reason for people to add it at the end and it is said by some young people but it sounds kinda old now.