I was so against the leaving to cry, I wouldn't even consider it despite DS being awful awful sleeper, but when DS got to 10/11 months, one night we ended up trying it. I was pregnant again, going back to work, and just exhausted.
I knew he was well fed, warm, dry etc... the problem was, he didn't know how to get to sleep in the middle of the night unless he was breastfeeding. So we left him to cry, and yes it was stressful and upsetting, and he got angry with us, and we went in every 5 mins to pat him (so there was only 4 mins crying in a row max, which you might get when they are in the car seat), and then after about 45 mins, the crying got less, so we went in less frequently, and after 90 mins, he went to sleep. He only woke once that night, and cried for 10 mins (again with checks) and went to sleep. The next night we braced ourselves for the same... he slept through all night!!! He had learned how to get to sleep on his own, and this made him so happy - you could really see the difference when putting him down for the night. From then onwards, we have had many many nights where he hasn't cried out for us. Sometimes he still does, and we go to him and pat him/lie him down if he's sitting up, and repeat checking every 5 mins, but there has never, ever been angry hysterical crying like on the first night, because now he knows he's in control of his own sleep. All he wants to do when he wakes up tired in the middle of the night is go back to sleep, and now he can.
I'm glad I didn't do it sooner than I did, but I'm also glad I didn't leave it later. Maybe don't rule it out altogether though in the future, if you are feeling desperate like I was. It's not as bad as you might think.