Why is just intonation bad?
Just intonation is extremely impractical for instruments that play chords (guitar or piano), or any instrument with fixed pitches which cannot bend, such as vibraphone or marimba. How many keys do you want in an octave on your keyboard? In the Baroque period, 12-tone equal temperament had not yet been invented.
Is just intonation better?
“Better sharp than out of tune.” Just intonation is, many believe, a more “pure” way of tuning and offers greater timbral and sonic possibilities than equal-temperament—the de facto form of intonation in Western music today. ...
Do orchestras use just intonation?
Yes, the strings of the strings section will be tuned to ET 5ths, usually, and generally the whole orchestra will play with a modern pitch reference (e.g., A 440).