If you are designing your own Magento Website on a Gateway Sites Platform that we will always provide you with a platform set up and ready with the default Magento Blank Theme
Although it is currently common practice to download the latest Magento stable edition, install it, and tweak the default demo template until it fits your desired look & feel this is not the best approach. The main problem is that the default magento template was not designed for this purpose. The default Magento theme was designed to showcase all the bells and whistles that Magento has to offer right out of the box.
Using the default theme is bad for SEO and it will not provide any advantage over the competition (it is very likely that your competitor has a Magento based shopping cart as well and it is very likely they are using a modified version of the default theme) If you start with the Magento blank theme you are probably much more likely to achieve higher ranking for similar catalogues than if you started tweaking from the default theme. This is mainly because the default theme has a lot more fluff than one really needs on every page, especially on the product pages.
Another reason why starting with a blank theme is preferred is performance - is it helpful to show 100+ products on the front page or does it make sense to help your users get directed to the right subsection of categories and help them find the product they really wanted to begin with?
In essence, if you start with the blank magento theme, you are more likely to avoid including unnecessary features on your shopping cart that hinder on the site’s performance.