Permalinks are an important key for search engine optimization. Bots such as Googlebot have gotten a lot smarter where they can index links even if they’re using a query, such as example.com/?p=535, but that’s not search engine friendly at all.
There are really two angles you can look at when setting up your permalinks.
The first angle to look at it is from the Bot’s point of view (“POV”). The bot is looking at the permalink and it first tries to recognize what that page is about by what the permalink says. If a permalink just has domain.com/article/798724, the bot knows that it’s an article and…well, that’s about it really.
But let’s say that you had something like what WLTC uses here: http://weblogtoolsc…gle-subscribers/. The bot knows that it’s about feedburner, google, subscribers, and that it’s an archived page on that site. Not to forget it also knows the date of the page that it was published — based on trusting the site.
The primary difference from the bot POV is that the more information you give it, the better.
At the same time, it’s really good to give a lot of information, but it’s also good to not overwhelm the bots. The default WordPress permalinks using the domain.com/?p=#### is not very search engine friendly (“SEF”) so that’s why almost all — most — sites will use the mod_rewrite to fix that.
The second angle is to look at it from a human’s POV but also keeping the bot in mind. I did that with my site and I found a happy medium. I went ahead and varied the permalink structure a little bit. I went with a year, article number, and article name — rather than the default year/month/day/article-name. I wanted to give my permalinks a better human readability but also provide the bots a functional permalink to know what the page is about.
As a concluding note, there are hundreds of trusted sites that don’t need to use this because of how well ranked they already are. Such sites include News.com, Time.com, there’s really an endless list, but for smaller sites such as blogs that on average won’t be as highly ranked (unless you’re Photomatt), the small things such as these changes can really help in the search engine result pages (“SERPs”).
But really, lastly, this is the BIGGEST FACTOR I can ever tell anyone.
Cool URIs don’t change.
Once you create a permalink, don’t change it, please. Cool links don’t change…ever. I mean it, don’t change it…please, it will create a more tranquil Internet for everyone.