Outlook clients are used to connect to the Exchange 2007 to access email. Non – Cached Mode clients can generate a significant amount of disk I/O traffic and affect the performance of the server. Forcing all clients to use Cached Mode can Improve the  performance

Below powershell forces to apply the same for all the users

Get-Mailbox | Set-CASMailbox -MAPIBlockOutlookNonCachedMode $true

Below power shell helps to apply for the Individual users

Get-mail username | Set-CASMailbox -MAPIBlockOutlookNonCachedMode $true