The only situation in which it isn't worthwhile is if you have nothing to add.
For example I saw BLF. Didn't bother reviewing because I had a great 10/10 time but there were already dozens of reviews saying that and also going through details in almost the exact way I experienced.
In that case it's pointless because I would have been spending my time writing something up that would have provided nobody with any new or useful information.
That is going to be pretty rare though and even when you see someone who's heavily reviewed, you will usually have a unique experience, so yes 90% of the time it's worthwhile
