Is it absolutely necessary to grout bathroom floor tile & new shower?

Yes it is. Over time those cracks and crevices will harbor soap scum and moisture and it will start to mold. You don't want that. Can you share a photo of what you have installed?

Hi Carla, I am going to put up a link to an article that has loads of good information on grouting tile but if you really want it here is what I found. If your tile project is in a dry area, you can install a specific kind of ceramic tile without grout. Use vitrified tiles, which are made of compressed clay dust, if you wish to install tiles without grout. Vitrified tiles are straight and square and can be installed butted up against one another without a joint.

https://www.rubi.com/us/blog/groutless-tile-installation/

Without grout, you are asking for trouble. Everyone's feet carry bacteria and in a wet environment, even soap will not stop the spread of it. The cracks harbor bacteria, mold and scum without grout and grout can be sealed (I reseal mine every 2 months on the first). It is very easy to clean! Every other day I spray my tile and grout with : 1 C water+ 1C vinegar + 2 drops of dawn stirred together. Let sit for a while. Rinse off and towel down. Be sure to caulk the corners!

I use this on my shower and never had a problem cleaning the grout.

Heat up 1 cup of white vinegar, mix in about 1/4 cup of Dawn Premium. Not the dollar store kind, because it is too thin. When mixed, pour into a spray bottle and fill with water. Shake. Spray down the grout and let it sit overnight. In the morning rinse. If you have stubborn stains, spray again. Use this mixture a few times a week. It will keep your grout and tiles clean. Also works wonders in the toilet bowl to keep hard water stains at bay. Oh you only have to heat the vinegar one time when you add the Dawn.

Oh, you need to use silicone caulk in shower or bath. here is a video which I tried and worked great https://www.youtube.com/watch?v=nHwmqkoz1tE

Yes, Grout, it gives your floor or wall a crisp finished appearance. it helps keep dirt and debris from getting in between and under your tile. It adds rigidity and strength to the tile installation.