In 2017-2018 it was a shame, ICO projects were able to buy their rating and get high scores.
Despite that, it's impossible to daily track the features of each protocol, so ratings are useful as an initial screening outcome. In addition, many crypto holders are not tech guys and have to trust third parties that perform code audit and rate the security level.

Consensys has developed a methodology for assessing risk in permissionless lending platforms, Codefi, that is an open framework for evaluating DeFi Protocols: https://codefi.consensys.net/defi-score

I am also working on a Defi APY tracker, using Codefi rate to make an initial selection of trusted protocols (here you can join our Yield Farming Survey).