There are downsides to making your heap too large, as when it comes time to clean up the heap or resize it, everything running in java must halt until the cleanup is done. The larger the heap, the longer it takes to do the cleanup.
I recommend you check your system by using this binding. It will give you advice if something needs changing via WARN messages in the logs. It will also allow you to graph the CLEANED HEAP size and will also report if a possible leak is detected before your system has an issue.
