Firstly, we need to define Technical SEO, as it’s often poorly defined and can refer to several different things, so let’s break it down into “onsite technical SEO” and “offsite technical SEO”.
Onsite technical SEO
The first purpose of onsite technical SEO is permitting basic access to your content (not blocking it conclusively) so that search engines’ crawlers can add your contents to their index.
The second purpose, which is often overlooked, is to make it easier and more rewarding for search engine crawlers to access your content. This can be done in a number of ways such as having a smaller file size, better content to code ratio, and more efficiently organised inter-page relationships (via linking, URL structure, breadcrumb microdata, etc).
On a deeper level, and crossing into the territory of holistic marketing, on-site technical SEO is very much concerned with quality of user experience and conversion optimisation in order to increase visitor satisfaction which increasingly stands out at being the most powerful ranking factor these days.
Offsite technical SEO
Offsite technical SEO is concerned with backlink profile analysis, especially link detox which is the process of removing and disavowing toxic links pointing towards your site in case a competitor is doing negative SEO against you or in case you’ve participated in unhealthy linkbuilding campaigns before. These toxic links can range from those which appear to be placed on good sites but in unnatural ways, through to those which may be naturally built but appear on spammy sites that you’d rather not be associated with.
The purpose of link profile cleanup (link detox) is to improve your trust factor and make search engines more confident about ranking your site well and giving you the benefit-of-the-doubt in case suspicious spam signals are detected in future. This ultimately makes your organic search performance more stable, secure and predictable (on top of simply ranking higher) which is always good for business.