What is the different between using synthetic sgRNA vs using crRNA: tracrRNA duplex?

When using sgRNA, there is no need for annealing crRNA and tracrRNA duplex prior to use. More importantly, several studies have showed that sgRNA has better stability than crRNA:tracrRNA when duplexed with Cas9, thus leading to higher editing efficiency^1,2.

1. Hendel, et al., Chemically modified guide RNAs enhance CRISPR-Cas genome editing in human primary cells. Nat. Biotechnol., 33 (2015) 985-989.
2. Ryan et al., Improving CRISPR–Cas specificity with chemical modifications in single-guide RNAs. Nucleic Acids Research, 46 (2018) 2: 792–803.