Total Blocking Time refers to the amount of time during a webpage’s loading sequence that the client was blocked from performing an action.
If a page renders & the user is able to click items or interact with it, there will be less Total Blocking Time than a page that renders but continues to load other items, making the user unable to interact until the other resources have loaded.
Generally, having a lower Total Blocking Time is advantageous as it enables users to begin interacting with your site faster, encouraging them to go further down your conversion & content funnels.
How To Reduce Total Blocking Time In Your Website Optimizations
Ensuring that the main thread is not held up by too many tasks as a page loads is the simplest way to reduce the Total Blocking Time in your page load sequence.
This means making sure that only essential tasks are taking place between the browser requesting the webpage & the Time To Interactive (when the user is able to perform an action).
In doing that, these essential tasks should be optimized as well to take the least amount of time by serving the fewest amount of compressed files as possible.
This way all requests will be able to be processed quickly, while not wasting time requesting more files than actually are needed to load the page.