For our ecommerce we can also choose to have a specific template developed from scratch, all of our own. As a tailored suit, it would have many benefits, among them high performance. This, however, if the "tailor" performs a professional job, otherwise like the woolen sweaters from the grandmother, we will have only an uncomfortable and ugly item of clothing.
A Custom Template , in addition to a high cost would present a poor scalability, we will have to resort to the developer every time our business grows and new features are needed and every time we have to update the CMS. With the speed of change of the modern market, such a solution is impossible except for ecommerce that bill hundreds of millions of euros, and above all they have to handle a huge traffic of users and have the necessary professional figures on their staff. In this case the choice is dictated by technical needs and CMS are not used, or if used they are completely rewritten. So in the jar of CMS such as Wordpress, PrestaShop, Magento, etc ... the best solution is a professional template, with the development of a Child theme that brings to the same a level of customization that makes it unique and very similar to a solution. Custom.