If you want to ride 350 miles in a weekend? You would be advised to use them.
I got a chuckle out of this.
As I've mentioned elsewhere on this forum, in September I did a roughly 270 mile/8 day trip across Wales. (With us getting lost it was closer to 300.)
The trip was awesome. Not 350 in a weekend, but it was an intense trip, and my first multi-day ride.
Before I left I kept getting advice to go clipless for the trip. I resisted simply because I didn't do a trip like that *and* be getting used to clipless at the same time. (And the words "nuts", "crazy" and "stupid" did get bandied about...)
On the fourth day, I woke up with serious bruising across the arch of my foot. Not only did I not go clipless, but I was also using plain old cross-trainers that were worn out well before the ride started.
So in Dolgellau (the next big town) we stopped off at the sole cycling shop and got some cycling shoes for me. The proprietor (a really nice guy) tried to convince me to get some pedals as well, even offered me a discount. But again, I resisted for the same reason.
At the end of the trip, the more experienced cyclist I was with (actually my sister) again urged me to switch to clipless, saying that I'd be in a whole other league as a cyclist if I did.
As soon as I got back to the US, I got some pedals and headed out. In that time, I've fallen twice: once the first time I got on the bike and the second time at S Neville & 5th as I tried to get past a car that was over too far. (Scraped the curb and fell.)
Now I can't imagine riding without them, even if I'm just heading down to the grocery store. Not sure I'm in a "whole other league," but I definitely notice a difference.