Should I forfeit?

I'm fairly new to this game (~40h). I see a lot of my opponents forfeiting (2v2) when their score is low, my teammates also forfeit quite often.

Even in a 2v1 situation, I never forfeit. Sometimes my opponents ask for me to forfeit. Is it rude not to forfeit a round you will most probably lose, maybe because it "wastes" people's time?

I don't forfeit because I use the round as an opportunity to practice. I don't really understand why forfeiting is an option anyway...

Thanks in advance for your answers!

Edit: I didn't expect that many quality answers. Thanks a lot to all of you for your instructive inputs!