Sealing tiles before installation differs from grout sealing because the tiles and grout are 2 separate components. Many types of porcelain or ceramic tile do not need to be sealed, but there are exceptions to this rule. Check with the tile manufacturer in this case. If your new tile is made from natural material, it will need to be sealed.
Tile made from marble, travertine, granite, terra cotta, or slate looks beautiful, but is susceptible to spills, stains, and chipping if it is not sealed. Many manufacturers do not seal the tile ahead of time, so try this simple test: shake a few drops of water on one of your tiles. If the drops turn darker or otherwise change color, the tile is unsealed. If the water drops do not change, your tiles have already been sealed by the manufacturer.
Grouting natural tiles before sealing them can end up giving them a foggy or cloudy look if grout gets caught in the porous surface. It is, therefore, recommended to coat each of your natural tiles with a silicone based pre-sealer before laying them and applying sealer, grout and or grout sealer. This will prevent this kind of discoloration problem.