Essential. Although I interviewed several therapists carefully, I still consider myself extremely fortunate to have found a very experienced gender therapist (gender clients going back nearly 30 years) and whose practice has been mostly trans clients for half her career. She has seen it all many, many times from people shopping for letters (which she doesn't accommodate) to gender presenting as a manifestation of other conditions, trans clients from childhood to quite elderly, tons of transitions, a few detransitions, spouse and family transition counseling, and more.
She did a careful and extended differential diagnosis, then proceeded down the path of sorting out co-morbid issues and depression before even starting to deal much with gender. As a result, I have the psychological issues under control (depression is still a challenge, but there's more involved than gender there) and I'm crystal clear on my cross-sex issues and identity.
The experience has been life-saving and transformative. She will participate in some company meetings when the time comes and also help with HR.
I had a less than stellar experience with another therapist after moving. Despite a few years of nominal gender experience (and a fraction of her practice at that), she just didn't have the depth or knowledge. I went back to my original therapist (above) despite having to travel.