Most cleaners and maintenance products will not harm the glazed porcelain tile surface. That said, it is also best not to use harsh chemicals frequently. If any acidic or alkaline products are used they do need to be rinsed and not left on the surface of the tile. Vinegar is acidic and bleach is alkaline, so you do not want to clean regularly with either one of these cleaners, in the case that you do, neutralize them with mild soap and rinse.
Clean regularly with warm water or Stonetech Stone & Tile Cleaner is a good cleaner for any tile surface. It is a neutral ph balanced cleaner. Rising after cleaning to remove any cleaner from the surface to avoid a haze build-up. As always follow directions on any product you use.
Porcelain tile does not need to be sealed, however, sealing the grout is recommended.
Bleach is not a recommended cleaner for porcelain tile. While it will not harm the tile itself (excluding some handmade materials), it will deteriorate the grout over time.
Always test an area prior to doing the entire area when cleaning and sealing.
Test the grout area to see if it needs to be resealed by applying a few drops of water; if the water stays in a bead form and does not absorb into the surface the sealer is working. If the drops spread out and darken or are absorbed into the surface the grout needs to be cleaned, dried out, and resealed.