Extremely fast eighth-note downstroke picking was used in the mid 70s and beyond by famous punk guitarist Johnny Ramone, who used the technique to play full live shows in high tempos (usually around 180 to 200 bpm).
This extremely demanding, then uncommon and somewhat innovative style contributed to Johnny Ramone's reputation as a guitar player, and it influenced many now-famous rock guitarists.
Downstroke picking has become a common technique in metal and thrash rhythm playing, notably exemplified by James Hetfield of Metallica (who has been regarded as 'the King of Downpicking'[1]), as well as Doyle Wolfgang von Frankenstein of The Misfits, Dave Mustaine of Megadeth, Kerry King of Slayer, Bobby Gustafson of Overkill, and Scott Ian of Anthrax among others.
If the guitarist has a difficult time keeping the strokes smooth, the quality of the music can suffer, often sounding sloppy or strained.
While down-picking in general is sometimes considered a good beginner's technique for learning at low tempos, it requires skill to perfect in faster applications.