Not every vendor needs the same level of review, and applying the full HSE assessment to a low risk supplier wastes time for everyone while slowing down the vendors who actually need close attention. Risk based vetting means deciding the risk level up front, usually based on the type of work, whether they will be on site and the hazards involved.
Each risk level then gets its own set of requirements, with low risk vendors covering the basics and high risk vendors going through the full assessment. The risk level should be reviewed when the scope of work changes, since a vendor that starts working on site may move into a higher category.