I look at BIAB as a bicycle with training wheels for people just learning about how to put a sing together. For someone who struggles with chord progressions, structuring a verse, bridge, chorus, half verse, etc... BIAB is great from the music side.

BUT....

When you are ready to move into the production side of things, Real Band is it. The way you can copy and paste chunks of songs is nothing short of an answer to a prayer.

Example. In my song Crying Private Tears, the chord progression is what it is, but the feel of the song calls for the bass line to ride a D when the rest of the music goes to an A. No matter how I set that chord sheet up as A/D, the bass line kept moving to A there. Enter Real Band. I copied measure 1, which was how it should be, and pasted it over the top of the wrong bass line for the 8 or so iterations of that progression. 2 minutes. On a 5 minutes song, that is 3 minutes less time than I would have spent playing it in with a bass guitar. With the ability to do gain changes, fades...... Created a solo in one song, For some reason one measure of the solo was way too hot. Highlight, right click, gain change, set up a -2 db change, apply... smoothed it right out. And at the end, the last sustained note ended too abruptly. Select the last measure, fade out, 100 to 0, apply... done. Just that easy.

Real Band probably won't make you Phil Spector or Mutt Lange, but it is cheaper than hiring either one of them. And it doesn't carry a gun like Spector....

No real reason to "combine". You have your choice. Most of us like Real Band better, but either one works just fine. Real Band is just more fully featured and far more flexible.