This grips my shit at the best of times- it's not hard to work out where you are up to on a thread- but I can see on a fast moving, lighthearted thread it saves a bit of time for those who can't be arsed but I've just seen a serious thread (relationship over etc) with a fucking full stop place mark (apologies if it was a posting error but the poster hasn't put anything else on the thread).
It's really rude to do that IMO - it's like saying I have nothing of any value to add to this discussion but I really want to watch it all unfold but can't be bothered to work out where I was in the story- that'll be a story that's turning the OP's world upside down.
I can totally see that not everyone has anything of value to post on a thread but does want to read it as they gave an affinity with it but place marking in that situation is horrible.
Rant over.