I think being able to join/divide lands in those parts of mainland (via support ticket with conditions) could benefit some users as not everyone wants a 1024 or group of lands to have something bigger.
Some benefits of this include the following
1 Show in search would be much improved on such groups of lands. 1 search and accurate traffic ranking for shops etc
2 Privacy settings would be improved especially for show avatars and access management where currently you would not see an avatar on other side of a building with show avatars unchecked and only 1 access list to manage.
3 Setting names, descriptions and land pictures would be far more easy.
Argument from LL when I have asked in past has been.
The mainland regions with double land impact in the parcels do not allow terraforming changes, including joining or subdividing the parcels as changes may cause accidental object returns elsewhere in the region.
But this is not correct as joining/ dividing wont change the total prim usage/capacity Only a change of owner of part would cause any items to be returned and only on your own land. Also many mainland bonus prim sims do allow join/divide.
Is also the issue of fairness as today an already joined plot was sold at auction and some others have been joined in the past and todays auction wouldn't have fitted in my proposed rules.
As for the rules.
1 All joining/dividing in the suggested regions would only be allowed via support ticket and done at LL discretion.
2 parcels should not be joined if they directly boarder other peoples land. Examples if you own 2 of a group of 4 you cant join if it will be bordering other peoples land but if you have a pair barely touching another land it could be joined (at LL discretion)
3 You can't have land split into smaller bits that where originally available in the sim.