I think it's okay to sit for some acts (not most) but it's hard to judge.
Example: I saw REO Speedwagon/Styx/.38 Special in June. Everyone sat for .38, stood for Styx, and about half and half for REO.
And when I saw Alice Cooper at the KS State Fair, everyone stood (to my surprise).
09/02 - Solstice
09/05 - DRI
09/09 - Origin
09/14 - Citizen
09/17 - Mineral
09/18 - Clutch