Outlook client basic authentication during migration

After reviewing the Exchange server migration guide the preparation to allow proxying from 2010 to 2013 the following command must be run on the 2010 server:

Get-ExchangeServer | Where {($_.AdminDisplayVersion -Like "Version 14*") -And ($_.ServerRole -Like "*ClientAccess*")} | Get-ClientAccessServer | Where {$_.OutlookAnywhereEnabled -Eq $True} | ForEach {Set-OutlookAnywhere "$_\RPC (Default Web Site)" -ClientAuthenticationMethod Basic -SSLOffloading $False -ExternalHostName $Exchange2013HostName -IISAuthenticationMethods NTLM, Basic}

My question is why does it call for enabling basic authentication for the client authentication method? This will cause all clients with mailboxes on the 2010 server to prompt the user for the password every time outlook is opened.

If I set the authentication method to NTLM will proxying still work?

Jose