Is scales practice really important?

YES!

Love them or loathe them there's no getting away from them. Scales practice is important... but not only for the reasons you may think! Practicing scales helps us think in a certain key. When we are sight reading or just starting to learn a new piece it is much easier to focus on the notes (and get them correct) if we know the piece is in Ab major and everything that entails, instead of trying to remember Bb, Eb, Ab, Db, Bb, Eb, Ab, Db and either forgetting some of them or constantly repeating the flats or sharps in our heads - which is rather distracting! Scales practice also help us hear tonalities, that is hearing what key a piece of music is in. This helps internalize music later on and also helps with memorization. It is much easier to memorize a piece when we are aware of which key each section is in and where it is likely to move next. All scales are related in one way or another.

Scale practice does not directly make playing pieces better. Scales practice makes your scales better. Practicing pieces makes those pieces better. Having said that scales practice does improves playing and therefore it does help your pieces in the long run. And practicing scales can be fun - in a challenging kind of way.

Scales help the fluency of your playing, your sight reading, improvisation, composition and aural (listening abilities) as well as being useful for practicing techniques on your instrument. Scale practice helps you hear different keys and tonalities and identify patterns within music. Scales you know well also give you the opportunity to practice techniques without having to think about notes. E.g. Playing a scale you know very well staccato means you can work on your staccato technique without worrying about the notes or fingerings. You focus on your staccato. Playing a scale pianissimo enables you to concentrate on making every note sound evenly when playing very soft. Scales practice can be used for much more than just practicing scales!