Well the simple answer is if you want to protect your stone floor from staining then you really should seal it.
One key thing you should do is to test your stone for porosity. To do this, add a few drops of clean water to your stone floor and if they are absorbed, the stone is porous. The image below shows a limestone floor with the water seeping in.
Sealing a stone floor gives you something called “reaction time” in that you have an opportunity to react and wipe up any spillages and any stain producing contaminants before they seep deeper into the stone. Anything that is water-based will be kept at the surface where they can be cleaned up a lot easier also. You typically have spent a lot of money on a stone floor so using a relatively inexpensive (in comparison to the cost of the stone) sealer will help ensure you get the most our of this significant investment and help keep your floor looking fabulous for many years.
If the Stone floor has been laid for a while then it is important that the floor is cleaned before sealing it.
My company West Cork Cleaning Services http://www.westcorkcleaning.com will do the whole job for you.