Seminars are the platform to meet the people with same interest and learn a lot at one clip with most material compressed in short. Some seminars have sessions where personal experiences are shared, which provide a great deal of practical information. Infact those are great morale boosters. If seminars are to be attended in foreign places, it can be a great vacation too.
Seminars also offer the ability to refresh old skills and also gain state-of-the-art information about various topics. Not having to devote more than a couple of days learning a new skill with others who share similar problems and needs is very useful. Most times you learn as much from fellow attendees as you do from the instructor.
Seminars also give you the opportunity, outside of work, to ask questions you might be too embarrassed to ask at work.