Why does my two engines have mirrored propellers?

[Maika]

When I bought my boat, the previous owner had mounted the port propellers on starbord drive and visaversa. This made the boat go in reverse when pushing the handles forward and visaversa.
The boat was beached, propellers where swithed to oposite side, and the controllers now worked as they should.
What is the reason for the drives having this setup?
Is there some advantages in having "mirrored propellers", or is it maybe just that the one gear has been turned around to make it easier to mount/run the cabels controling it?
(I am looking at replace them with electric engines/drives, and wonder if this is something I would think of when ordering propellers.)

[RonaldL]

The wheel effect is reversed