Sony A77 electronic first curtain shutter
No, I don't think that you ever need to turn electronic first curtain off...
You will think so if you personally encounter an exposure anomaly that disappears when EFCS is turned off. Numerous examples of such anomalies have been posted in this forum and elsewhere in the recent past. Uneven exposure across the frame is just one such anomaly. In some cases this might be explained by improper diaphragm operation, but in no way does that explain all documented EFCS problems. Sony has not been forthcoming with a complete description of causes behind all the possible issues.