As long as you won't be sacrificing an ide optical drive already having a sata model in that won't be any problem. Eventually I'll dump the ide cd burner here already having a sata dvd burner in already.
With the extra drives in however you will tend to restrict some air flow inside the case especially if you use a flat ribbon type cable. Many would simply go for a larger sata drive or add on an external model for seeing a bit more storage available.
In fact someone lately was seeing 5 external usb drives in use on one system! Here I would have simply grabbed a single 2tb eSata external drive and called it a day.