This will display Blue Highlights (lines or circles) when the cursor is aligned with another Control Point, Center Point or End Point of another object on the design as you are drawing or moving objects.
This can aid when drawing/moving if you need it to be aligned with other objects in the design.
If it is too distracting, this can toggled off under Options.
Auto Alignment Definition
The Auto Alignmentfunction displays bluealignment lines as you move an object and it lines up to another object in Designer,Traceand Nesting, making aligning openings easier.
This can be toggled on/off in the Options menu for Designer and Trace.