I won’t go into to much information in regards to the process of developing and optimising an application that uses live tiles. The reason for this is because I am not an expert when it comes making applications on any platform. I do know that using the live tiles feature on an application is very important as it’s a key selling point for Windows Phone and your applications.
I also know that it can impact the battery live, which is generally bad as we do love to use our Windows Phones for as long as possible. The article that I am going to recommend in a minute has been designed for Windows 8, however I believe that the same rules apply for Windows Phone. You will always need to “…try matching or better yet, surpassing … [competitor’s] battery runtime achievements on light/low load use.” when creating an application for Windows Phone. So you will need to “Treat all your “Metro” apps as if they are always running (but at zero impact to battery/performance).”
So check it out and see if it helps you with your Windows Phone applications and if you’re making Windows 8 applications. Well then it should also help you there as well. You can find the complete article from the msdn blog.