My first webinar was in 2011, chosen through Writer's Digest because they were professional and had great course offerings. I loved the medium so I participated in webinars on topics as diverse as querying, common core, middle grade novel openings, and character development. I learned a ton cost-effectively and without leaving my office. Then, in my role as co-Regional Advisor for SCBWI-MI, I worked with co-RA Leslie Helakoski and with Aaron Brown from Delve Writing on creating a 5 part series of webinars (From Manuscript to Submission) for others to view. That's when I realized how effective they are for diverse audiences.
The trump card for webinars from my perspective is that I found my agent, Jodell Sadler, through one. She offered a picture book pacing session through Writer's Digest, and after I submitted a picture book for critique as part of the webinar, she requested more information about my writing and eventually, I signed with her. <insert happy dance>.
Bottom line (ha!): webinars rock. Go forth. Sign up for a webinar nearest (or far-est) from you. You'll be glad you did.