But the question is not whether high kicks are practical in a general sparring situation, TKD_G. The question is whether they are useful in a close-quarters self-defense situation against an unsought attack by a dangerous, but likely street-savvy assailant who's probably not much more than a foot away from you, and when every other avenue of escape from the situation has failed. I can snap off a roundhouse kick to something like my own head height, and I'm 6' tall. But not when the target's 14" or less away from me hand has just grabbed my shirt or thown a haymaker at me from that distance.
When things are close in, lower kicks and knees are probably your best bet. Then again, that's my training- don't throw out all high kicks. However, if it works for you, then it works for you. I'm not saying it's just flat out wrong, it's just my personal prefference, it just isn't what I'd do when it's all up close and personal.
However, like Kacey said, if you don't train it, then it's a good chance it wouldn't. To each his own...