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