Add-PSSnapin Microsoft.SharePoint.PowerShell
$site = Get-SPSite -Identity https://yourwebapplicationURL
$site.Url
$site.WebApplication.WebService.CoauthoringMaxAuthors=19
$site.WebApplication.WebService.Update()
$site.Dispose()
Write-Host $site.WebApplication.WebService.CoauthoringMaxAuthors
The main purpose of the co-authoring is to limit the users for editing the particular document in document library .If the document is editing by too many users then users looses the UI experiance instantly ,So we limit the users interaction with co-authoring
