Not true. Inode-based filesystems with antifragmentation code such as
ufs and ext2 suffers a dramatic loss of performance due to increased
fragmentation when running for an extended time in the near-full
configuration. Part of the function of the reserved space is to make
sure there is enough free space to let the block placement algorithms
work efficiently.
UFS usually reserves 10%, ext2 5%.
There are cases, such as news spools, where fragmentation is not a
major issue since the files are so small anyway. For news spools it
is safe to turn this value down quite far (I use -i 2048 -m 1 for news
spools.)
-hpa