From a consumer standpoint, Totalbiscuit is right. Pre-ordering represents nothing but a risk to the consumer, except in cases where availability might actually be a concern. That usually only comes up when talking about games that come with some kind of physical addition (i.e. collectors editions) or international console/handheld games that receive limited distribution. In those cases, pre-ordering does reserve you a copy in case supplies run out on the whole. In most modern cases though, digital distribution, Amazon, and robust supply chains for retailers pretty much prevent this from being an issue in the normal case. You're almost never in any danger of not being able to get a copy of the game if you just buy it normally, whether at launch or not.
Additionally, the pre-order culture means that publishers have been putting more and more stock into advertisements to drive pre-orders than actual content and polish for the game. There's a psychological instinct in people to get more invested in something after they put down money on it. It's dangerous because it makes you less objective when assessing the quality of something, and can cause you to become a partisan for it before you even play the game, as you want people agree with you to validate your purchase. It perpetuates the hype cycle, where hype gets generated because people were hyped and now more people are hyped and what they were hyped about to begin with gets lost. This also means that people tend not to cancel pre-orders or get refunds even if there's a bad state at launch due to them having already bought in.
However, there is truth to what PikeStance is saying about the industry right now. Pre-order culture is so ingrained that companies use the pre-order numbers to plan for the game's future and support before it's even released. Simply put, the market has signaled to them that this is how it going to relay it's will and it's been mostly consistent about doing that, so a game that gets lots of pre-orders is a game that's going to do well in their eyes and deserves attention. That means that games that get big pre-order numbers start getting additional resources and planning put into them right away, sometimes even adding things before launch that weren't going to be there earlier just to increase the value proposition and keep the good press going for the sake of more pre-orders. Meanwhile a game with low pre-orders may have its support/content plan stagnate or be cut short because it's assumed to underperform.
At the end of the day, it's a bad situation. Pre-order culture has become the norm because it worked too well for too long, and now we're kinda stuck with it unless it crashes spectacularly, at which point there are going to be more than a few innocent casualties. My personal suggestion is to not take part and just let the pre-order campaigns play in the background. There are enough people out there with far less attachment to their money and a lot less consciousness of this stuff that the system will go on, but it also means there's no need to worry about the health of any given game before launch. The only real guarantor of success should be a well made game, so reward that, regardless of if it pushed pre-orders or not. Don't punish quality just because it had to dance that dance.
Unless of course you think that the physical bonuses of the collectors edition are worth the money. At which point, hey, all power to you.