What is "Plans" for?

[Zeiss Ikon]

In 1.6.1 RO, specifically Kerbal Construction Time, there's a tab that's new since I played RO in 1.4.1: Plans.

What is it for and how do I use it?  I haven't seen any indication of streamers using it, at least that shows in their YouTube videos (not that there are a lot of 1.6.1 RO videos anyway).  There has to be a reason for it, but it's not clear what to put there, how to do so, or what I gain by it

[Zhetaan]

8 hours ago, Zeiss Ikon said:

In 1.6.1 RO, specifically Kerbal Construction Time, there's a tab that's new since I played RO in 1.4.1: Plans.

What is it for and how do I use it?  I haven't seen any indication of streamers using it, at least that shows in their YouTube videos (not that there are a lot of 1.6.1 RO videos anyway).  There has to be a reason for it, but it's not clear what to put there, how to do so, or what I gain by it

Here is the relevant post:

And this is the concise version:

 

Edited February 3, 2020 by Zhetaan

[Vanamonde]

Modding question moved to the modding subforum. 

[Zeiss Ikon]

Ah, thanks @Zhetaan -- the "concise version" is a little too concise, but the first answer you linked gives me enough to at least know where to look to figure it out.  Blue button at the top in either SPH or VAB lets me put  craft into the "building plans", then I can start a build from anywhere I can see the KCT menu button.  This ought to be a significant time saver for those times when you need to launch the same design serially (like when playing without reverts and trying to get past repeated engine failures, or during the sounding rocket era when you just need to launch the same rocket with, perhaps, an edit of how much sounding payload is aboard).  At the least, it'll save the (non-trivial) load time to get into and out of the editor(s).