Can't comment on A7 specifically (I shoot Canon), but I usually use live view when on tripod because of EFC. I'll generally compose with the viewfinder (to save battery juice) then switch to live view for the shot. Not only serves as mirror lock-up but uses EFC, so no movement other than the diaphragm until the exposure is ended. I've always wondered why electronic shutters have not become the norm - I used to assume it was a speed issue, but then the Nikon 1 came out with faster shutter speeds on electronic than mechanical (1/10,000 vs 1/4000), so that's not it. If anyone knows what the advantages of mechanical shutters are, I'd like to know.