There are 2 good usecases with transparency mode:
1. is already described: hearing to announces, short talks (not so nice imo)
2. phone-falls: with transparency mode I cannot only hear my own voice but also is the background noise almost cancelled. Without transparency you cannot hear your own voice while talking, that is distracting…
-> Your experiences? I still have to get used to it – think my no. 1 headset still will be AP (normal) or the plug-in EarPods.