Hi John. In order of importance from my view. You will notice that I may have things that just never get stated as key important items. Since they have been there for so long, we tend to over look them. Plus I believe in controlling the inventory and being able to state "I know where everything is and where is came from, etc. That this is available to anyone."
1) FOOTPRINT. Which will always take you back 'home' to Endevor. Where the source is. No matter where the member is located. Whether a load, jcl, etc. Extremely key to audits. Which when running reports, you can see if there are exceptions, etc.
2) SMF recording. Which in combo of all the recording done in Endevor itself, pretty much covers the statement "No one can do anything in Endevor without an administrator knowing about it".
3) ACMQ and just component information in general. Plays a key role in many things. Package validation etc. But I think its best usage is for the developers to know what was brought together and from where when they compile their programs.
4) LISTINGS the LL option which would seem a standard thing by now. Where capturing the listing of a compile and/or link is noted in the component info and allows the LL option to work. A fantastic feature for the users and administrators when one has to review things. Instead of looking at the users job output or some other location. One doesn't miss it until its not available. Unfortunately my shop doesn't do this. Noticed it on day one when I came on board. Tried to have it addressed, but failed. Instead they had us put them into DDIO files. Ugh. Why not both? Who knows.
5) PDM. Even though this is a companion tool, its very important and useful. Again, don't have it you miss it. As far as I know, its the only tool that works with Endevor. Three way compare, inside Endevor, outside libs or a combo. Then use the info to create a new combined body of code. My shop never turned it on, which I keep telling them they should.
6) CONTROL for consistence. Meaning the inventory structure and especially the processors. Ensuring what was used last month is the same now.
NOTE a drawback related to this. For administrators. Processors of course are versioned. But the inventory structure, especially processor group definitions, symbolic overrides, etc are NOT versioned. An issue we have mentioned over the years to be addressed. We all have to use some sort of work around.
7) QUICKEDIT. Its name says it all.
8) SDLC via multi Endevor environments, stages via mapping etc. Allows for parallel development etc. If one has an administrator that 'thinks' out of the box. Endevor can be flexible in its configuration. This would include the 'sandbox' approach.
9) PACKAGE which of course allows for different methods of promoting changes through the SDLC.
10) ESI. Not normally mentioned, again you don't miss it unless not used. My shop uses a home grown thing. But really, ESI is much more flexible and maintainable.
Good luck.