You know what happens if you don't. When you are done, you look at your beat up filthy hands and ask "Why didn't I just put on gloves?" As simple as it sounds, hardly any builders apply a sealer on new tile. Go ahead and ask them. I have. They just say no and shrug their shoulders.
Clear Seal is the most basic protection you can give your new tile and grout. It affords a level of protection by penetrating into the grout with molecules of different sizes and staying there to protect against the intrusion of dirt and liquids. That dirt and those liquids are what cause the stains over time and sometimes you can't get them out. The grease that gets into the grout eats away at the grout over time, as well. It's a chemical reaction that takes place. It can be prevented by applying Clear Seal over a clean surface every 2-5 yrs as needed, depending on wear and tear.
Yes, you still need to clean. Clear Seal does not change the appearance of the tile and grout and you wouldn't even know it was there unless you tested for it like I do before I do any work. Clear Seal keeps dirt and grime from penetrating deep into the grout lines and makes clean up quite a bit easier. In fact, if a quality sealer was applied when the surface was new, then clean up would easily make the grout look brand new without the stains that sometimes can't be removed even by my equipment and methods.
This beautiful home is several years old. The owner had the foresight to apply a sealer when it was new. The tile and grout still gets dirty, but my equipment cleaned it all up super fast and it looks brand new. Clear Seal, at a minimum, is a must!