Optional means very little.
I see huge amounts of APIs where 1 or more (often lots) fields are optional.
When I look at usage of those APIs invariably the optional fields get populated, typically with the mindset of "even if we don't directly use it now we might in future and / or it could be useful in data analysis to improve our algorithms". There has been a long ingrained culture of grabbing and storing as much data as possible, the only way to stop it is to prevent that data being sent.
.. Not that "targeted" ads work well anyway - so a lot of slurpage is counter productive - lots of adverts for something I have recently purchased (and is the type of item I will not be likely to purchase again for a long time (e.g. fridge, oven etc.) is just irritating (but shows that detailed content data on pages I have been visited is used (arguably abused) by ad slingers: I am not affected by ad slingers seeing the tedious home appliance, IT etc. web pages I visit (but object in principle) - but plenty of people will be visiting sites that deal with potentially sensitive health, political, religious etc areas & it's really not a good thing that ad slingers can gather such knowledge (e.g. many countries have nasty approach to non heterosexual behaviour, ad slingers selling on their "inferred" LGBT lists to such countries could have unpleasant consequences for those listed)