We found that FXCM servers, although online on Sundays, were sometimes no up to date, so some price data was missing. This seemed not to have happened anymore recently, but FXCM does not guarantee the consistency of their price servers during weekends and holidays.

So my answer is: It's theoretically possible that restarting at weekends does not affect performance, but it's not guaranteed.

To tell the truth, for our own trading we've never experimented with restarts so far. In fact none of us even ever got the idea to intentionally stop and restart a live trading software. We have some Zorros here running for more than a year, still in version 0.9. So all what I told here is rather theoretical, we have no practical experience of restarting effects and side effects.