From Biter experience the sort of sites you have to do remedial work on are not blazing fast some common problems I see are : using unoptimised images adding

From Biter experience the sort of sites you have to do remedial work on are not blazing fast some common problems I see are : using unoptimised images adding massive amounts of javascript messed up canonicals internal links requiring redirects to add or remove trailing / terrible design choices - oh yes lets put 10 products on a single page