Yes, we use this expression very often. You know some of its meaning exactly but the meaning can be 'it would/could be..." or "it would have been' . 저녁을 같이 먹으면 좋을 텐데. (I wish we could have dinner together.) 성적을 더 잘 받으면 좋을 텐데. I wish I could get better marks 어제 만났더라면 더 좋았을 텐데. It would be better if we met yesterday.

in case you are well prepared some tasks or handle topic well, you never use this sentese this is when someone did wrong,and mass up.they saying this one. 여기 식당이 있었을 텐데........but now reality is not.so use this for excuse or cover up mistakes.