The ever-present conundrum of learning a musical instrument: do you play what you want, i.e. favorite pieces and new additions to your repertoire?
Or must you (as you hear over and over again that you absolutely must) play scales, whole tones, double-stops, chords, etc. in order to keep fiddle fit?
THE TEXAS SCRIBBLER 
I can only forward to you the answer all my piano teachers gave: yes. As painful as it is.
Actually I do both exercises and repertoire. Most people do. I just think the cartoon is funny.