It’s certainly not required unless you’re a tutor or teacher here. If you’re looking to make friends in the community or find “language partners,” it is indeed best to fill out your profile as much as possible. Not necessarily with a profile picture, but saying a few words in the “introduction” section lets people get to know you a bit and can help attract like-minded individuals. A profile picture is just one way of introducing yourself. Note also that the decision to use, say, a bowl of fruit as a picture can say as much as an actual photograph. If you’re interested in professional lessons, you don’t need to fill out your profile, but I like when students send me a personal message explaining their linguistic situation and giving me some idea how I can help them improve their communication skills.