PCA is so fast that it can run on 100 million data-points and give you results in minutes with the proper implementation of it. If you can find a way to projec

PCA is so fast that it can run on 100 million data-points and give you results in minutes with the proper implementation of it. If you can find a way to project that new data quickly, and if the decision boundries are instantly recognizable to us humans - one can draw the boundary faster than a model could generate it given the data. The human drawn boundary has bonus regularization built right in too (because "sub-optimal" boundaries on the training data may generalize better)