A laser beam is perfectly straight by definition, making it more accurate than a tape measure. That is also why a laser measurement taken at an angle returns a longer value: An angled line to a plane is longer than a level one. More often than not, this level horizontal distance is the measurement you need.
This fact of geometry can be a problem on active sites where stacks of materials, machinery or other obstacles prevent a level horizontal measurement. The longer the measurement, the greater the error.
In Smart Horizontal mode, DISTOs use the reading from an angle sensor to correct a measurement taken at an angle. The result is an accurate level measurement even if you have to aim over obstacles on the job site.