One benefit of being in fellowship with God is peace. In the midst of the storms of life, we know that He's there, that He loves us, is compassionate, and that He will lead us through the darkness (we will always see light at the end of the tunnel.)
Another benefit of being in fellowship with God is a sense of purpose. When we serve God and others, our life has true meaning (there's a reason for us to be here.)
And what we do in life has eternal value.
When we have a relationship with God (through faith in Christ Jesus as Lord and Savior) we have hope. We have hope in the future for we know that one day we will be with our Lord Christ Jesus in heaven. We do not fear death, for death is just the door to our heavenly home.
Being in fellowship with God, also, gives us a sense of God's love as we walk with Him. Isn't it great to know that God loves you, approves of what you're doing, and is concerned, and active, in your life?