Besides the cleaning aspect, we use denatured alcohol in our alcohol lamps for singeing and for 'heat flowing' the finish which I don't recommend for the faint of heart. The heat flowing is something Lee (our master rod finisher) has used and she has developed a particular technique over the years and it scares the crap out of me; but that's another blog.
Anyway, I do use the alcohol lamp for singeing and sometimes if I'm not careful with my tag trimming, I have to deal with that piece of nylon thread sticking it's ugly little head out from under my wrap. Curses!
I use this technique to avoid the tag end:
Cut your thread at a angle with pulling pressure from you tap end fingers. I pull with my left hand and push the thread back against the thread line from where it was pulled under and then using a #10 scalpel I pull the blade across when the thread meets the wrap.
If you do end up cutting badly and have a tag end, singe it with the alcohol lamp, let the thread ball cool and then you can take your burnishing tool and by applying pressure against the melted nylon and it will usually snap off. No matter whether you have a thread ball or not, I always burnish the thread wraps and I always burnish from outer edge to center of wraps.
The thread wrap is rotated/moved continuously through the flame, and I don't spend more than 1/2 second for each wrap! It doesn't take a lot of heat to ruin your thread wrap or even damage your blank. Be very cautious and careful when you are singeing.
By tilting the lamp it is sometimes easier to see the flame. I always put a dark background behind the lamp to see what the flame is doing. Alcohol flames are very clear and hard to see and that is a problem if you are not aware of the flame. You can leave the heat on the wraps too long very quickly.
Never use anything butt Denatured Alcohol for fuel; do not use rubbing alcohol.