Think of it as a workout. The harder you workout the longer or more intense your relaxation has to be.
A professional athlete has to train hard everyday so they need to have get a massage and/or ice bath to allow for a quick recovery. An average gym goer doesn’t need to have these because it will take a week until he/she will train the same muscle group.
How long is your event? How many speaker are there and how long is each session? How long are the breaks? How “heavy” is the content being presented?
A 3-day technical conference with 2 coffee-breaks and a lunch break requires a totally different rejuvenation strategy than a 3-hour personal development seminar.