Is there any additional sealing operation required after grouting for the bath shower
All Portland cement based grout benefit from a sealer.  I prefer the distillate based sealers, but I hear good things regarding the newer water based sealers.

One grout type doesn't need any sealer: 2 part epoxy grout.  A bit more care and effort during install, but nearly bullet proof afterwards.  Shower floors and foyers really stay clean.