In the Canvas preferences, you can define behaviours relating to zoom as well as how things should appear on the Canvas.
The animated zoom will provide context from where you have zoomed from. If off, your document will update to the new zoom level with no transition.
Zoom In On Selection
When you tell Sketch to zoom via the View › Zoom In / Zoom Out commands, Sketch will by default zoom into the center of the Canvas. By selecting this checkbox it will instead focus in on the selected layers.
Zoom Back to Previous Canvas Position
Using this option, Sketch will zoom out to the position you had on the Canvas before you started zooming in. By default when you zoom out, Sketch zooms back straight from the center point currently on Canvas, but if you scroll around a lot while zoomed in and you expect to return to the previous position on zoom out, select this checkbox.
The color selected in the preferences will be visible if the smart guides option is enabled, and appear when layers align, or when measuring whilst holding the Option key.