If you have users that are still using IE to visit your SharePoint 2013 sites, they may encounter an IE message telling them they should install the latest version of Silverlight (which is quite dead). All this is really used for is the gallery for installing new apps/webparts. This can easily be disabled by running a bit of PowerShell (by disabling this, users will still get the fallback functionality as you would in Chrome, etc.)
$webapp = Get-SPWebApplication http://sitename //check to see if the Silverlight prompt is enabled $webapp.allowsilverlightprompt //if it returns as true, then set it to false and update $webapp.AllowSilverlightPrompt = $false $webapp.Update()