I wouldn't even think about attending a shooting school where I took vacation time and spent somewhere around $2000 for tuition/ammo/travel/boarding..... without taking a back-up gun that was very similar to my primary. What would you do if your gun went down on day #1 ? Sure you can carry spare parts, or maybe the school has a gunsmith on site, but this all takes time that you are supposed to be getting the training. I have only had to use my backup once. I had a malfunction, cleared it and found that the bullet had come out of the case and filled my action with unburnt powder. Gun wouldn't run reliably. I ran to my truck and got out the back-up which I shot until lunchtime when I could clean my primary.
When I was shooting IPSC semi-seriously I was firing sometimes 1000-1500 rounds a week. After awhile I pretty much always had one gun down with a bad extractor or ejector. I wasn't making a lot of money and sometimes had to wait until next payday to order parts. So, I had a backup gun. I switched back and forth between the two constantly.
I recently took a pistol class and discovered that my primary gun was having problems due to wear. Luckily I had a back-up and a back-up for my back-up. I had the on site gunsmith replace some stuff on my primary on day one of the class and was able to use it for the remainder of the class.
Two years in a row I went elk hunting and had a sight failure on my primary rifle during my final zero check days before the hunt. Yes, I since went to a different sighting system after the fact, but, I had a back-up and got my elk both years.