We can see a common phenomenon in both of the algorithms: for the first few thresholds, the phrase table becomes smaller and smaller while the translation quality is not much decreased, but the performance jumps a lot at a certain threshold (16 for Significance pruning, 0.8 for BRAE-based one).
the Significance algorithm can safely discard 64% of the phrase table at its threshold 12 with only 0.1 BLEU loss in the overall test.