It'll make no performance effective difference.
I would counsel against it, as a defrag hammers the FAT
(file allocation table - an area of the disk which contains information on what files are physically where on a disk
) and CF cards have a fixed read/write lifecycle.
However, it ain't all doom and gloom with CF cards. Some cards employ on the fly remapping
(so I am led to believe
) which will map out sectors or areas that have had too many writes, such as the original fat, and replace them seamlessly. Others contend that the life cycle of writes is in the order of millions before problems occur. Either way, I ain't losing sleep over it