Chokes can be very dangerous. One watches TV shows like "The Unit" and they routinely use a naked choke to put people to sleep and they hold it for several seconds after the person goes limp. They recover without any problem. The author has never tried that so it might be realistic.
The authors experience is that people being choked sitting in seiza begin to hallucinate as they lose consciousness. They start moving around giving the impression they are resisting. Because they are resisting Nage chokes even harder. Usually Nage figures out that Uke is passing out before Nage goes limp. Nage lets go and in a few seconds Uke starts coming back to consciousness. This is accompanied by considerable jerking and thrashing around. It is quite scary! It seems that Uke must have permanent brain damage. Kodokan Judo has techniques to help someone who has been choked out.
Students should learn to choke and be choked standing. That way Uke can learn what if feels like to be choked out. When standing Uke's knees get weak as Uke begins to lose consciousness. That makes it easy to tell when to quit and Uke can learn the feeling.
Chokes can also damage the spine in the neck. Some chokes and all head cranks are designed to break the neck. It is a good idea to do front and back bridging, resist choking yourself with a gi belt, and other exercises to strengthen the neck muscles.
In freestyle and most Kata pull the chin down to tighten the neck muscles and make the neck difficult to access and shrug the shoulders up to your ears. Sometimes Uke makes the neck accessible to help train Nage.
These warnings should not scare you away from choking your partner into submission. When you practice really being choked you get very tough and you learn how to really choke. Really choking is necessary to be proficient and taking chokes is certainly part of Aikido.