I used the cruise line for my first 2 river cruises (both in Europe, and both not adding on any additional days). In both cases, I was flying in on day of embarkation. For my other 2, both in south east Asia, I made my own arrangements and added on time at the beginning of the cruise. (On the Irawaddy, I added on the cruise lines post-cruise extension, but made my own air arrangements.)
Now I have much more difficulty with jet lag, so I will never again fly in on day of departure.