I found the videos in this article very helpful to understand Enter Sends Messages in N1MM. I admit that I've never fully understood the concept before watching these videos and now plan to use this feature in future contests.

Here is the excerpt from Ward Silver's excellent weekly contesting letter:

What is "Enter-Sends-Mode" (ESM) anyway? Offered by several contest logging program, this mode lets you do a lot with the Enter key. Call CQ? Press Enter. Send the exchange? Press Enter. Acknowledge the received information and ask for more callers? Press Enter. Pioneered in the MS-DOS TR-LOG program, many top operators find it to be efficient, but it does take some getting used to. To explain ESM, the N1MM development team has posted links to videos on using it during CW and RTTY operation. (Thanks, Larry K8UT)

I'll have to check out the videos, but "ESM" is what made TR such a great program. Once I got used to that method of operating, I couldn't go back to CT - I have been invited to operate at multi-ops and asked what software was being used, turned down the invite solely because it wasn't an "ESM" program. N1MM's implementation is a *little* different from TR, and I don't remember exactly what it was, but it was easy enough to get back into the feel of using it. But it is extremely efficient.

The other huge advantage TR and N1MM had over the others (don't know if others have implemented it or not as I haven't kept up with in over the past few years) is for operating Sprints: TR and N1MM can automatically send the proper exchange based on whether you're CQing or answering a CQ - and those messages definitely should be in different formats.

All of which reminds me...I've got to update N1MM on my laptop...