Any part of your business operations that requires constant end-customer facing task is an essential part of your business whether its customer service, technical support via chat, email or phone.
Some jobs/tasks require specific knowledge, skills, and experience that can’t easily be gained through simple training such as website design, article or copywriting, etc.
Although customer-facing tasks is essential to an efficient customer experience, tasks being done in the background is as important such as document processing, data entry, etc.