This reminds me of the task-killer debate on Android. If it makes you feel better to close the apps, then by all means, do so. However, the OS does a good job of managing memory and killing apps as needed.
Is there a benefit to this? Battery? data usage? speed?
Every other day or so I go through and close apps that I used that I know I only use once in awhile to free up RAM. If something crazy happens or I feel the system is dragging I go and close them all (sometimes reboot too) to get it back to butter smooth.