Having sand mixed into the grout gives the grout extra strength to keep it from cracking.
For grout joints wider than 1/16” you’ll want to use sanded grout. Having sand mixed into the grout gives the grout extra strength to keep it from cracking (the same way that gravel helps make concrete stronger). Most floor tile installations will use sanded grout.
For grout joints thinner than 1/16” (typically on walls and sometimes on countertops) non-sanded grout will work just fine. It’s also easier to work the creamy, non-sanded grout into smaller grout joints.
Picking the right color for your grout is one of the biggest challenges. The printed colors shown in grout brochures will be a little misleading. We almost always recommend buying a small quantity of several grouts and doing some real-life samples
For floor installations, some tile contractors we know will actually pour dry grout over small areas of the floor, sweep it off the surface and get a sense of how the different color grouts will look in the actual setting. (The advantage of this method is that they can then just vacuum the dry grout out once the decision has been made.)
But dry grout will not have the same color as the same grout once it’s been mixed, applied, finished and then left to cure. So when we’re in doubt about the color we take some leftover tile, glue it to a scrap piece of plywood, and actually mix up the grouts we’re considering, apply them, let them cure, and THEN make our choice.
Our other bit of advice about grout colors: don’t use white grout on a floor or countertop. It’s hard to keep clean. A light gray grout will keep up its appearance better.