I use split grade alot. Les McLean's elegant explanation made it clear for me. I like the control it gives me over burning and dodging for my "maybe this could go in my portfolio" prints.
The postcard exchange? We're talking small prints that are going to be scratched and banged up in the mail. Pick a negative you like, that doesn't take a lot of burning and dodging or other fiddling to print well.
Read up on split grade, then try it with a negative you are having a hard time printing with a single filter. My eureka moment was an image of water splashing over black rocks. Burning and dodging the dark shadows on the rocks and the splashes and specular highlights of water and wet rocks was driving me nuts, and making baaaad prints. Split grade got that neg under control, and taught me how and when to use split grade.