There are two really good reasons to learn and practice scales and arpeggios. One is to develop strong fingers and controlled, even playing. This evolves over time to controlled, even playing at high speeds. The other great thing is it helps to learn and understand different key signatures.
Why is it important to practice scales?
Practicing scales every day will greatly improve your skill on the piano. Not only do they increase your instant awareness of key signatures, but also build powerful finger muscles and muscle memory. Gradually building up speed in scales will transfer to speed in pieces of music you play too.
Are arpeggios important?
Arpeggios create a fast, flowing sound. Besides using them for speed in playing, arpeggios add a kick to improvisation skills. Because an arpeggio contains all the notes of its chord, you can use them in your solos and link them to what's going on in the chord structure beneath you to create cool-sounding licks.