Combined Harvesters

Is it me, or have you ever actually seen two or more harvesters combined? I mean, I have seen them on their own, and in herds in big fields, on telly and in books...but they are never combined.

When they combine is it like in Transformers when the robots combine to make a bigger robot...or is it something altogether more...shall we say...sexual? For what purpose does the combination take place?

I wonder if it is like baby pigeons...we know they are out there, but no one ever sees them. I mean, there are always more harvesters, so presumably they must combine at some time...maybe they have masonic lodge type meetings where they combine in utter secrecy.

It is a mystery to me. But then so is how we decided to call yellow 'yellow'. Ho hum.