When you create, place or relocate elements or components in your Revit model, Revit uses a predefined set of snapping dimensional increments. For example, when you are drawing a wall and you move your mouse from the start point to the end, you will notice the temporary dimensions increasing be certain amounts, these are the Snap increments.
If you would like to adjust the snap Increments, go to the Manage Ribbon, and select the Snaps tool. This will bring up the Snaps Dialog Box.
You can adjust the Snap Increments for Length and Angular control. You can add as many increments as you like, they just need to be separated by a semicolon.
The different numbers help you control the increments when you are zooming in your views. For example, if you zoom in on your model to look at a detail, then Revit will adopt a smaller value, if you zoom out in the same view it will adopt a bigger increment value. It works off a screen value of 2mm. (There is a little tip on how it works at the top of the dialogue box, under the Dimension Snaps title.)