Always include a fade! :)
Let's say a track ends at exactly 10 seconds. Instead of just setting the track length to 0:10.000, also include a brief fade. Perhaps a half a second, a full second... whatever sounds best to you.
Why bother fading out during silence? Because without the fade information, sometimes notsofatso looks to the "Stop after X MS of Silence" setting under the 'Config 3' tab. This may sound okay to people using the default setting notsofatso has, but the problem with the default setting is that it is too short and actually prevents you from hearing parts of songs or entire songs from some nsfs. (A good test is to listen to the plain nsf for Alamana no Kiseki / Arumana no Kiseki, there are no tracks of silence, but the default setting in notsofatso will skip over some tracks)
So for people tagging NSFEs or listening to NSFs regularly, that setting needs to be changed much higher to make sure you're never missing anything. And as such, if you listen to an NSFE track without a fade on the end, sometimes the abrupt ending turns into something like 5+ full seconds of silence.
There are also other players than notsofatso that support NSFE (rockbox, and an upcoming nsf flash player), as well as an NSFE -> M3U converter, and it's not totally certain how all of those will also handle an abrupt ending without a fade. So, to err on the side of caution, setting a fade should help guarantee that the timing comes out the same for everyone.
It's not a big enough issue to go back and fix already uploaded NSFEs I don't think, but it'd be a good practice to pick up for newer ones.