Is there any benefit to mixing red and white wine togther? I'm no expert on Rose but it appears that it is not necessary either red or white wine.

My question is historically or even now is there any benefit / interesting flavor combinations that are made through mixing various ratios of various types of red and white together?
Your question seems to be based on a false assumption. Rose is not a "mix" of red and white wine.

Red wine is produced by (red) grapes which have their skins left on during fermentation, white wine is produced from pealed grapes (of any colour).

Rose is produced by extracting the skins (or red grapes) at some point in the fermentation process. 

It's a common misconception! 

Source: Napareserva



To answer the clarification in the comments:

Often wine is blended to bring in the best parts of different grapes:


  The goal in blending is to bring together wines that don’t stand alone to make a wine that is superior to its parts. There is a big difference between blending, which is meant to improve your wine, and mixing, which is intended to make something — like an off-flavor —go away. Source: WineMaker


Personally - being brought up to appreciate good wines - the idea of mixing red and white is blasphemy. They are just too different and therefore do not follow the "rules" laid out in the link above. 

However, I did find evidence that it has been considered - I imagine you could end up with a wine very similar to a Rose if you got the balance right. I'm not sure I can really credit that with being a "source" though.

This answer has been asked elsewhere though and, although I don't often like to just copy and paste an answer from elsewhere but the last paragraph seemed exactly what you are looking for:


  Rosé is popular nowadays and some producers do mix red and white wine grapes in order to satisfy demand, it's all about business, after all, however, such wines tend to be made of not very high quality grapes because there is no point in mixing the grapes or wines of premium quality together since they will cancel out their flavours anyway. Sometimes, producers will add some extra sugar to the mix in order to balance out or mask the shortcomings of taste that appeared due to mixing the products that are not supposed to be mixed.


The post also goes into more detail about why they are generally too different.