Sketching is important when designing a logo but I do not believe it is a must. It allows the creativity to flow out of ones head onto paper, or computer depending on what you are sketching on. Many graphic designers were artists on paper and canvas far before they took their passion into the digital world, so sketching often comes naturally for them. Sketching allows artists to get to the creative process much faster, so it is a tool just as much as the computer or design software.
When I started as a new designer I sketched more because Adobe software was new to me and hindered my creative process. As I gained experience the faster the creative ideas came to me so I felt less of a need to sketch. After 12 years of experience I am able to take what clients want for their next ad or logo and translate that into my Adobe software. Although, still to this day I will sketch logo ideas due to complexity and customization required.
During the logo design process I am able to take those sketches and translate them into the digital world for clients to use in promotional/marketing materials. Although sketching is not a must, sometimes it is good to get ideas out on paper even in this digital age.
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