That's what it's there for. I've had people say that it was spot on and a few say it was off by 10-15 minutes at times. It really depends.
That said, it should be a good tool when you're in the parks (and planning) to get a feel for crowd movements and if you should make the walk from Pirates over to Haunted Mansion or just hit the Jungle Cruise.
No wait time apps/sites are going to be 100% accurate unless they constantly have a person going through each and every line throughout the day.
Even crowdsourced wait times apps can suffer from a lack of data (people not entering recent enough times), incorrect data (people not entering the correct time), or surges (people entering a 10 minute line before a flood of people come over from a parade or fireworks).
That said, to each their own!
P.S. Thanks for using the site! It was a weekend project that turned out to be helpful to quite a few people.