v0.7.0 adds the option to disable many of Qrack's optimization layers, in the system-specific optimal layer stack, (which is bimodal, depending on the presence/absence of OpenCL devices). For many specific circuits of interest, significant additional performance can be gained by disabling one or more Qrack layer stacks, if one knows the characteristics of their workload, as regards the attempted optimizations in Qrack.
(However, the default case, with _all_ optimizations layers on, is designed for best general performance based upon developer experimentation with realistic and/or high-entanglement universal circuits. It is expected that users will most commonly best benefit from leaving all optimization layers on by default, and not considering v0.7.0 options at all, without a reason.)