The answer is yes, it is useful for therapists to seek their own therapy. My experience is that even though I am trained to identify underlying patterns with respect to my patients, it is often hard for me to turn the microscope to myself and my patterns. I may self-reflect a lot, but I often need another, objective person to help make meaning of what I am feeling/observing. I use multiple, trusted sources to help "keep an eye" on me. 

My definition of a therapist is someone who cares for me and is not afraid to challenge me. Ideally, this person is also trained in identifying and interpreting patterns of human behavior. Objectivity is the key word here. Family members may be able to support and care, but often are not able to step back enough to be emotionally objective from the situation. Thus, when a marriage is in trouble, people who care often take sides and typically end up adding to the mess.

Similarly, I may not be able to hold an objective view with my own children. On several occasions, I have asked myself, "I am a trained therapist who works with other parents. So, why am I not able to handle this situation with my child differently?". Of course, I know the answer. And, this is when I consult with my therapist sources. Sometimes, I do not like what they tell me. However, I am ALWAYS grateful because I can trust them to turn on the 'light switch' for me.