This depends on the brand of bougie you're using. In at least one brand, if you bend the distal six inches or so, it's impossible to bend back into the original shape. At best, you end up with the tip oriented in a random direction, e.g. sideways or upside down. You can't really compensate for this when you have a poor visualisation, so you risk bouncing off an arytenoid, or simply can't find the right angle.
Despite a number of concerns being brought forward, one of the services I work simply puts a bend in them in the end closest to the operator, where it has less of an impact. Unfortunately, I still end up throwing out a few dozen every year, because the tip has got damaged.
This isn't a problem with every brand. Some of them are more elastic than others, I guess.