planned everything, what's the point of praying?"
"Do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God" - Philippians 4:6, ESV
We see times in Scripture where God changes direction due to the prayer of others. There are occasions where nothing happens and others where the miraculous happens... both are answers. Jesus is even seen praying numerous times throughout the Bible. One thing is for sure, when we fail to take time to pray, we begin doing things in our own strength, instead of relying upon the strength of Christ. This is a grievous sin and a major hazard to your spiritual health.
More information about prayer:
http://carm.org/topic-prayer
http://www.gotquestions.org/why-pray.html
http://www.blueletterbible.org/search/search.cfm?Criteria=prayer&t=ESV#s=s_primary_0_1