This page contains random notes on filesystems.
Some modern filesystems (ZFS, btrfs) support transparent compression. If you have the CPU to spare, this can make a world of difference. If you are on magnetic hard drives (which commonly get saturated), you lessen the amount of data stored on physical disk and lessen how long it takes to read that data. This can result in significant I/O increases. If you are on an SSD, you store less on disk and drive the cost per storage lower.
A FS that supports copy on write (COW) will not physically copy bits when a file is copied until the copy changes. Even then, it is often intelligent about only writing the bits that changed. Someone told me that the page cache is even smart enough to not duplicate the memory until it changes. I haven't confirmed that and am not sure which file systems/kernels that applies to (hopefully all).