Because it's technically accurate (instead of guessing if plots are separated by a fence/hedge/wall) & the cadastral parcels are sometimes inaccurate, making the OSM data better than HM Land Registry.

Hello, what prompted you to make this change, along with changing the [boundary] and [admin_level] for the regions or councils in Berkshire in your changeset_count 271 through 278?

reverted in changeset/161639344

I believe this is incorrect. admin_level=10 is reserved for civil parishes, which High Wycombe is not. Community boards are not civil parishes but constituted by them or in place of them, hence admin_level=9

Monkey Island is upriver in Bray

way/23679577

I'm also suspicious of this park node in Dedworth, which seems to describe an adjacent road rather than a park

node/11819999712