This approximation yields improved results at the cost of CCSD. In particular, DCSD equilibrium structures are as accurate as for CCSD(T), see
D. Kats and F. R. Manby, J. Chem. Phys. 139, 021102 (2013);
D. Kats, J. Chem. Phys. 141i, 061101 (2014);
D. Kats, D. Kreplin, H.-J. Werner, F. R. Manby, J. Chem. Phys. 142, 064111 (2015).