Confession coming... Toward the end of this ride, a little mean streak surfaced and I bet a fellow ride leader riding beside me that the rider up front was going to miss the turn. When the turn approached, it seemed as if he was going to take it, but then kept riding straight. Here is where I should have yelled "RIGHT". Instead, I silently pointed the right turn and made the turn with the remainder of the group and let the "wrong way riders" figure out they goofed.
While winning a bet is always nice; this scenario, unfortunately, is actually all too common. So why is it important to know the route?
First, and foremost, knowing the route is a matter of safety. If you are up front and don't know the route, you can endanger the riders behind you. I have witnessed several instances where a rider up front doesn't know what to do when a navigation choice is required. All of a sudden they are slowing and weaving out of their line while they try to find out what to do. The riders behind are then at risk of potentially running into the front rider or moving too far into the road.
Second confession... This happened to me once and I was the cause of a minor incident with one of the riders behind me crashing. Fortunately it was a minor incident and the rider and bike were OK. In this case I knew the route, but there was construction and I didn't recognize the street until too late and I tried to make the turn anyway. I slowed unexpectedly and caused a rider behind me to overlap wheels and fall.
Secondly, knowing the route is important should you end up riding on your own. If you get dropped or even have a mechanical issue, you may find yourself separated from the group. You should know the route so you can safely get home or catch back up to the group at a break stop. Knowing the route may also allow you to take a shortcut to get back with the group. Some riders are very skilled in using shortcuts to avoid a challenging part of the ride and still remain with the group for large portions of the ride.
Garmin Edge 520 and I love it. These devices are amazing and a great asset to a ride. However, they are not a substitute for knowing the route. I consider them to be an enhancement or an added tool for following the route.
Cycle Folsom makes it very easy to learn the route. Every meetup notice has a Ride With GPS route linked that can be reviewed. If you do not have an account, simply sign up - it is free. Then follow the link in the meetup ride description and you can examine the ride. I like to click through the cue sheet as this will show me all the turns. I will also note the planned break location(s) and any climbs.
Ride leaders take the effort to provide a safe and well planned ride. Part of that effort is creating a route and making it available to all riders in advance of the ride start. Show them some courtesy in learning the route and doing your part to ride safely.