When I work on my designs in Eagle I usually set grid size in mils. It is convenient for me because most of the PCB manufacturers I use specify minimum trace width and distances in mils. Then, when I place some component, this component is aligned to the grid - its cross fits the grid. Therefore, routing traces is easier and whenever a trace goes to some resistor or capacitor pad, this trace is also aligned. That helps with better looking thermals and other stuff. However, when I am changing board dimensions or placing mounting holes/drills I switch to mm based grid. If I forget to change it back afterwards, place additional components and then switch to mils, these new components won’t be aligned.
I could change all of the new components parameters - x, y positions to be precise and match them to the grid I use. However, the following trick is faster. Just try to move the new components with ‘Ctrl’ key hit. The component will be automatically snapped to the grid and you are good to go again.
