slow and fast scale a Tidal pattern's time by a factor, changing its speed without altering its structure

The slow n function stretches a pattern so it takes n cycles to complete, and fast n (alias density) compresses it to fit n repetitions in one cycle. slow 4 $ sound "bd*2 sn" plays the pattern at one-quarter speed. fast 4 plays it four times per cycle. Since slow 0.25 = fast 4, the two functions are inverses. Both apply to any pattern, including control patterns: slow 8 $ saw stretches an oscillator wave over 8 cycles. Combined with every, they create periodic time-scale changes: every 4 (fast 4) $ sound "bd*2 sn" speeds up every fourth cycle.

Examples

// quarter speed:
d1 $ slow 4 $ sound "bd*2 [bd [sn sn*2 sn] sn]"
// four times speed:
d1 $ fast 4 $ sound "bd*2 [bd [sn sn*2 sn] sn]"
// selective: every 4th cycle goes fast
d1 $ every 4 (fast 4) $ sound "bd*2 [bd [sn sn*2 sn] sn]"

Assessment

What does slow 0.25 sound like compared to fast 4? Explain why they produce the same result, then describe a musical context where slowing a pattern is more musically useful than a rest or silence.