I don't know if it necessarily needs to be every day, but it needs to be at a consistent cadence, whatever you decide that cadence is, and at a consistent time of day (after you do some analysis on what time most of your views are happening and tailor to that). I personally schedule multiple videos ahead of time to release every other day at 10:30 am eastern and i say this on my videos so my viewers know exactly what to expect (Of course I recently learned this lesson and wasn't doing it during my ealry videos). On the other hand, I've heard that Casey Neistat is in favor of daily uploads and he grew much more when he started doing this, but as others here have mentioned, there are other factors to consider.