Many, many years ago I was at the annual Doug Fike Match at the RCMP depot. I watched a shooter who had flown in to Regina from the Northwest Territories for the weekend for the match, then on Monday he was flying from Regina to the US for another match. 2 stages into the match his gun went down big time, it was unrepairable without the help of a gunsmith. He had no backup, so he wasted a day and a half in Regina watching everyone else shoot, then he flew to the US to WATCH the match he was to shoot in.
I've been shooting competitively since 1986, I've had 3 handguns, 2 shotguns and 2 rifles break down on me during matches. When your shooting 5-7 stages in a day you don't have time to repair your gun on site. Backup guns are CHEAP INSURANCE when you sit and consider the cost of gas for a 26 hour drive to a match, 2-7 nights in a motel, food, match registration, etc that it cost you to get to the match. I'm personally not going to waste my time and money to watch a match, when I've paid to participate. If your shooting IPSC, you need only 2 guns, but if your shooting Cowboy action, your looking at at least 3 spares.