Maybe the OP could come back and clear this one up. Maybe it was something from the other "railroad forum" he mentioned.
I'm not the OP, but I'll do my best to explain.
When traveling southbound on the Coast Starlight to a connection eastbound on the California Zephyr, Amtrak uses Sacramento as the transfer point. The CS arrives at 6:15 AM. The CZ departs at 11:09, almost a five hour wait. So, many people ask to connect in Martinez, as the wait is shorter.
A few reasons come to mind why MTZ is a better choice:
1) You so not have to get up as early
2) you may enjoy breakfast in the diner, as it is served after departing SAC (on the Starlight, of course)
3) there is not much to do in SAC at 6:15 in the morning, and the station benches are not very comfortable.
4) you will have more time on the train, if you like
Of course, if your southbound Starlight is running late, then all bets are off, and you should make your connection in SAC.
I have done the SAC connection twice, and both times the CS was early into SAC. I wish I had made the reservation to MTZ
If you are not up for taking any chances, then just wait in SAC for the CZ.
Hope this helps