SharePoint Applications should be warmed up in the morning before the Director launches your new SharePoint App. Why? Web Applications will recycle overnight and will no longer be resident in memory for fast page loading; it is usually an important member of the team who notices it, the Director. He will come to you and say the Farm is slow, speed it up. To avoid this situation run a scheduled script that will launch popular or important sites into memory ahead of time resulting in no one noticing a slow running web page.
Here is a PowerShell script that is designed to work in SharePoint 2007, 2010 and 2013. Comment out/in the sections that apply to your Farm. Set it to run as a scheduled task in the Windows Task Scheduler, for an appropriate time, shortly after the App Pools Recycle and before the important users starts using your system, typically at 5:00 AM.
If you have a load balancer in place, use IP addresses instead of the host header name. You may have to adjust your IIS settings to allow your site to respond to IP address directly.
Here is a link to my Script