Tape speed / recording quality. Frames on VHS are diagonal stripes from one edge to the other. At lower tape speeds, those stripes get shorter and closer together. The horizontal resolution is unavoidably reduced. Color information gets muddy, because that’s some deep magic in a black-and-white signal. Adjacent frames can bleed into one another. Worst of all, you’re more likely to get tracking problems, where the ridiculous wheels-in-wheels of the diagonal / helical read mechanism get misaligned with the stripes, and the whole picture can drop out.
You wrote a really long and interesting response that completely failed to answer the question. What’s SP in this context?
I think we used a different term for it, so maybe that’s a regional abbreviation. But I’m thinking they were talking about the recording quality/speed. I remember there being two options, one gave you twice as many hours but the quality was lower.
