My answer depends on yours.

If you know the key, set it first.

If you are just making up a progression to woodshed over, then as soon as you know a key, even one that’s close, set it in the key signature when you can. Did you notice when you click on C to change the key signature, there are two columns? The left side changes the key signature and changes the sound, transposing to the new key. The right side just changes the key signature without transposing.

Why does this matter? BIAB uses the key signature to make decisions. For example, is that note or chord going to show as a G# or an Ab? I have read that it also makes a difference in the sound but I cannot prove that.

By the way, welcome to the forum.

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.