It's a bit sad that a lot of motion designers don't know how offset works, even though it's one of the most powerful loop types After Effects has to offer.
According to the After Effects expression language reference
, offset "repeats the specified segment, but offsets each cycle by the difference in the value of the property at the start and end of the segment, multiplied by the number of times the segment has looped."
In plain English, loopOut('offset');
repeats an animation, starting the next loop at the last frame of the previous loop. That is, the object keeps moving in space, offsetting
the next cycle while maintaining the difference in the property value.
Say you animate a layer to rotate 0 to 90 degrees. In the next cycle, the layer rotates 90 to 180, then 180 to 270 and from 270 back to 360—or, you could say 0—degrees. Forever and ever…