What's the point in the backup slot if you write raw to only one slot? I always write raw to the both. jpeg is basically useless for me. If I buy R5, I'll be writing raw to the both slots as well.
Well, there are several situations where you will want to write rw in one card and jpeg in other.
For example Photojournalism, sports or weddings. In this type of works I always shoot jpeg in one card and raw in other.
- Photojournalism, sports: First...security, if one card fails you still have another one. Second, in sports or photojournalism you don´t edit the photos, you don´t have time to do it, so you deliver the jpeg file. So jpeg is your primary files. Raws, you save them if you want to edit a photo to make it more artistic for example. Or also for security, if you fail very bad the exposure or the white balance you have the raws to save the day.
- Weddings: Usually I save in one card the raws and in other card jpegs. Why? First security (If raw card fails at least you still have the jpegs to save the day...) and second speed. Sometimes the couple asks you to make a fast presentation in the end of the day and you dont have any time to edit. So you choose some of the best jpegs and put it in the computer. Fast and simple and a happy costumer.
- In wildlife...It depends....sometimes I don´t write in both cards making copies, i do prefer to use both cards writing because I very often fill both cards. If I am on assignment i always carry my laptop so in the dead periods when nothing happen often take of the cards and make direct copies to ssd drives. One at the time..of course cause in wildlife we know how fast and unpredictable are the moments. So, as i make almost instant copies i dont need to make dual raw writing.
But I understand what you are saying, and if you dont make photojournalism, sports or that wedding services, so it´s a good idea to shoot raw to both cards. We never know....