The best thing to do is use the smallest grout line your particular tile will allow and get a grout that closely matches the tile.
Marble subway tile grout line.
If you are going for high contrast or retro style wider grout spacing gives you the opportunity to make a statement with your grout.
Grout lines for floor tiles.
Most floor tiles are 8 inches by 8 inches but larger versions are available.
How to grout marble tile.
As a general rule floor tiles should have grout lines of 1 8 inch or larger depending on the type and size of tile.
For most granite and marble tile i install i use either 1 32 or 1 16 inch grout lines.
Because of this minimizing the width of grout lines is advisable.
Note that using the smallest grout possible will increase installation time.
Although tile installations can be installed in groutless format the traditional method calls for grout to be placed in the joints between the tiles.
If smaller spacers like 1 8 are used it will accentuate the size difference of handmade tile.
This is true of man.
This thickness leaves room for the natural variation in.
Finished grout lines will vary from 1 16 to 3 16.
In most other tile i will use 1 16 or 1 8 inch lines.
Grout including sealed grout tends to wear more quickly than tile and become more porous and prone to staining.
I try to use the smallest grout lines the tile will allow.