http://penny-arcade....lains-why-stret
PAR chat with Andy Schatz of Monaco. He's not a fan of stretch goals. I'll just copy-paste my reddit comment:
It's a bit of a sweeping and generic statement though. Many developers will have ideas, grand and magnificent, on what they'd love to do with their game, and they need to balance it against how much they think people would provide for a kick starter. So they'll budget for what they need in order to make the base game, minus all the trimmings, and offer that up for the masses on Kickstarter. If they get more, and that can be likely, it means they can put in more of the features they'd wished to do. The other option being budget for their grand design and offer that to Kickstarter at the much higher budget that they might not receive.
Also in many cases you can also offer up stretch goals that don't affect the gameplay; hiring in a proper/better musician, expanding to more platforms, revamp of art styles, release of source code, creation of level editors, etc. Or just don't offer any at all (as was the case with FTL, though that was early days).