When a directory is created on a Solaris 8 platform it has a size of 8k. If you add a lot of files to that directory then that 8k will get expanded to cope. If you then delete most of those files the directory will not shrink back to 8k which is what
bruceb3 points out. However, we are only talking a few kilobytes here and you are probably not going to have lots of directories all with enough files to cause the expansion. So I agree with your SA that it's not going to gain you much. If you contemplate a filesystem where there are going to be huge numbers of very small files (or symlinks, perhaps) you may run out of inodes before you run out of data space so consider reducing the bytes per inode when making the filesystem with
newfs. Conversely, if you have a files system that has just a few large files, perhaps database files, increase the bytes per inode, thus creating fewer inodes and leaving more space for data.
Cheers,
JohnGG