Just letting water sit isn't acceptable for most tap water.
Read @bookshelf's answer.
Note: personally I use Amquel and Novaqua instead of Prime.
edit: hey @book. I use those mostly out of habit, and because I've never had an issue when using them. But also because I used to do a lot of bleaching of decorations/dead corals, tanks, equipment and the such.
A big squirt would hasten the de-bleaching process, reduce the risk of poisoning the tank. We bought them by the gallon.
Other water conditioner chemicals are mostly crap (as you know).
Damn I hate Aqueon.
Remember, I did this as a business. One of the other techs at a company I sub contracted to, killed off a 200 gallon tank by accidental poisoning with bleach. I had a client's pesticide guy spray a pile of dead coral she was bleaching in the sun on her patio. There's lots of ways people screw up.
My complaint about Aqueon is that they never invented anything. Everything they make they knocked off/stole or copied from other manufacturers and had made cheaply and badly in China or Asia. They're ruining the hobby.