How to prevent site owners to create sub site

If you agree that we should keep sub sites at minimum, the PowerShell script below can help to prevent site owners to create sub sites.

This script also revoke the "delete historical versions" permission from contributors. That's what I do for almost all site collections.

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction "SilentlyContinue" 


# remove "DeleteVersions" from "Contribute" 
# remove "ManageSubwebs" from "Full Control" 
function ChangePermissionLevel([string]$SiteUrl) 
{ 
 $web = Get-SPWeb -Identity $SiteUrl 
 $contributePermissionLevel=$web.RoleDefinitions["Contribute"] 
 # $contributePermissionLevel.BasePermissions="ViewListItems, OpenItems, ViewVersions, ManagePersonalViews, ViewFormPages, Open, ViewPages, CreateSSCSite, BrowseDirectories, BrowseUserInfo, AddDelPrivateWebParts, UpdatePersonalWebParts, UseClientIntegration, UseRemoteAPIs, CreateAlerts, EditMyUserInfo" 
 $contributePermissionLevel.BasePermissions="ViewListItems, AddListItems, EditListItems, DeleteListItems, OpenItems, ViewVersions, ManagePersonalViews, ViewFormPages, Open, ViewPages, BrowseDirectories, BrowseUserInfo, UseClientIntegration, UseRemoteAPIs, CreateAlerts, EditMyUserInfo" 
 $contributePermissionLevel.Update() 

 $FullControlPermissionLevel=$web.RoleDefinitions["Full Control"] 
 #[System.Enum]::GetNames("Microsoft.SharePoint.SPBasePermissions") 
 # $FullControlPermissionLevel.BasePermissions="FullMask" 
 $FullControlPermissionLevel.BasePermissions="ViewListItems, AddListItems, EditListItems, DeleteListItems, ApproveItems, OpenItems, ViewVersions, DeleteVersions, CancelCheckout, ManagePersonalViews, ManageLists, ViewFormPages, Open, ViewPages, AddAndCustomizePages, ApplyThemeAndBorder, ApplyStyleSheets, ViewUsageData, CreateSSCSite, CreateGroups, ManagePermissions, BrowseDirectories, BrowseUserInfo, AddDelPrivateWebParts, UpdatePersonalWebParts, ManageWeb, UseClientIntegration, UseRemoteAPIs, ManageAlerts, CreateAlerts, EditMyUserInfo, EnumeratePermissions" 
 $FullControlPermissionLevel.Update() 

 $web.Dispose() 
} 

ChangePermissionLevel "http://sharepoint/sites/demo" 

rm function:/ChangePermissionLevel 

Write-Host "Finished! Press enter key to exit." -ForegroundColor Green 
Read-Host