Whenever tile has a right angle like that grout is prone to fail so caulk is used.
Gap between tiles and wall.
The tile council of north america recommends at least a quarter inch gap between the tile floor and the walls.
Get photos of great finish details include photos with bid and contract.
Your walls and floors are pretty stiff but there can be movement between the two that will crack the grout.
Ceramic tile wall gap back of tile should rest on finished wall.
The overall finish of your job really does depend on your own personal style.
For smaller tiles is advisable to use small spacers.
Tile stores generally sell caulks that match the grout.
This will give you say a perfect 3 8 caulk line with an irregular wall to counter gap.
If you have tile on the wall adjoining the tub select a caulk that matches the color of the grout.
Instead fill it with an elastic material capable of sustaining the movement of the floor and the movement of the wall.
You can try and maybe nothing will happen but if it cracks you will have to dig it out.
Therefore the spacing is predetermined and usually averages 3 16 to 1 4 inch.
Your tile person will take the largest gap and run a tape line using that as the thickness or the caulk.
The line will continue maintaining caulk gap regardless of the gap of the wall to counter.
Fill gaps up to 1 4 inch in width with caulk.
Never fill this gap with grout because tile grout is not flexible.
The large format 18 inch tiles should have inch space in between.
Current trends are moving towards leaving much smaller grout lines between tiles.
Caulking is the best choice for this application.
When you install ceramic tile on the floor you must take care to create an expansion joint between the walls and the tiled floor.
If your gap is smaller than 1 8 inch in width use.
As the tiles increase in size a larger gap becomes acceptable.