It helps to seal natural stone, but it does you no good whatsoever to seal porcelain or ceramic tile. It can actually cause you problems since ceramics are pretty much non-porous, so instead of penetrating into the tile, the sealer will just sit on top. If it dries it can leave a haze.

Matter of fact, most sealers have a warning to not get the sealer on the tile, and if you do, wipe it off before it dries.

Many grouts are modified, they come with anti-microbe this and polymerized that. Still, grouts can benefit from sealing IF they are in a harsh environment.

I wouldn't seal wall grout in a dry area. You can seal floor grout, but it's best to just chose a non-white color and give it a good cleaning when it needs it. If you had a nasty area like a well-used mudroom on a pig farm, then an epoxy grout would probably be a wise choice.

In wet areas like a shower, personally, I don't seal grout. You'll not find many installers who do. Most tilers leave it to the homeowner to seal, because in many respects, sealing grout can be of dubious value. My opinion.

When would I seal grout in a shower? If I was installing natural stone. I recommend natural stone be sealed, so it's a no-brainer to seal the grout at the same time.

If you do seal in a wet area, use a breathable sealer that allow vapor transmission.

In my own house, none of the bathrooms have sealed grout. I didn't seal the grout in my laundry room floor either. The only grout that is sealed is on my foyer floor, because...it's slate. I wanted to seal the slate, so the grout got hit at the same time.

mongoct,
Thank you very much for your informative answer. This puts my mind at ease.
I will not seal anything then. Now for the grout, it will be a gray color, is their a particular brand you recommend.For the octagon-dot floor and subway tiles in tub area do I just buy any kind of grout.