This trick (by Sumit Rai) was published in Linux For You (LFY) under the Tips And Tricks Section. Sharing it with all the Linux Geeks out there 
When you format a partition in Linux , 5% of the total space gets reserved for privileged processes, by default. This is done so that system processes continue to function correctly ,if the filesystem gets full. This is useful for your ‘root’ partition.However if you have let us say 50GB separate home partition, you may want to make use of few additional GBs by reducing the percentage of the reserved space. You can use tune2fs command to change the default allocation of space reserved for privileged processes. Command for the same is :
#tune2fs -m 1 /dev/sda6
Here we have changed space reserved for privileged processes on /dev/sda6 to 1 percent. You can use your device file according to the target partition instead of ’/dev/sda6′ . You can see the effected change by mounting the filesytem and checking available space using df command before and after you execute the above command. This command is quite useful in so called ‘Emergency’, so do remember it
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can we use it for / peartition
Thank you, very helpful
Thanks for the reminder, I’d been meaning to do this for some of my storage space. Frees up an extra 37GB on a 2TB drive.
You should probably mention that this will only work on ext2, ext3 and ext4 file systems.
info tune2fs:
NAME
tune2fs – adjust tunable filesystem parameters on ext2/ext3/ext4
filesystems
Dude! pretty sure most of us folks running linux have a journaling file system, hence ext3 or ext4,,, So lets just say, if you are dumb enough to not know what filesystem you have and you run this on an HFS or NTFS system. Be sure to run a sudo rm / *.*
So Doug, If you have to mention what filesystem this works on, I’m sure this command is not for you.
So it should be more like, Linux geeks only!
but linux geeks might be using a journalling filesystem such as btrfs or reiserfs or many many options; the ext3 and ext4 aren’t the only journalling fs options, plus this command works on ext2 which isn’t a journalled filesystem at all. this in fact has nothing to do with the journalling behaviour and that 5% space is reserved for the root user, for use in just that emergency which you mentioned
I tried a similar idea using gparted, and unallocated space I had no use for and bricked my install.
very vague description for a so important thing.