I do not see what all the fuss rhythm. Why I should not use the 241 BPM (for example) if the program let me do so, and no significant adverse impact on the normal human form?
It's to avoid slight variance in note length, which happens when you use tempi which clash with the NES's clock-speed of 60 ticks per second.
Being a seasoned performing musician, I actually think it's way more important to choose a tempo that feels right than to use a tempo which is perfectly in sync with the NES clock. In some cases, you can do both, but certainly not always.
It's also necessary to consider what note lengths you're using. 150 tempo is fine for 32nd notes and 96th notes (which are powers of 2 and 3 respectively), but a simple 1/5 note yields 19.2 frames.
The biggest problems with tempos that don't match the NES clock is that it can screw with two-channel echo delay effects, which I use fairly often. Using 150 BPM and changing only the speed will sometimes make it much more consistent. Unfortunately, even then I get artifacts from time to time (due to phase cancellation, it seems).
