My question is sort of specific - I'm trying to find airfare from SFO to Japan. The nonstop fares are quite expensive from SFO, but MUCH less expensive from Los Angeles. I'm considering buying a separate tkt to and from San Francisco to Los Angeles in order to take advantage of the better LAX-Japan fares. Did anyone have a similar experience or might offer some useful suggestions?
Thanks in advance.

I live in NorCal and mostly fly out of LAX to both Europe and Asia. I usually find better fares, and more options from LAX.

You can always fly down to LAX on Southwest if the 'legacy' airline's fare is too pricey.

I always use the website Kayak to see who's flying on my route, and then I check the specific websites of those airlines to see what kind of deals are offered.

If you decide to fly out of LAX, then be careful that you allow enough time to make your connection. If both segments are ticketed together, then you are protected. Otherwise, you may want to arrive a day earlier. We have some wonderful Japanese restaurants in the city of Torrance, fairly close to the airport, where the national Toyota offices used to be, and many expats wanted authentic food.

I'm with janisj about this. I live in NorCal (near Sacramento) and have flown out of LAX many times to Australia and Europe. Southwest has inexpensive flights from NorCal to LAX.

And you might look at one-stop fares (with the stop being LAX) on your preferred airlines. Sometimes that makes a huge difference in fares.

Where do you live? If you fly AA, very often the fare SMF > LAX > european or asian destination (so all on one ticket/protected) will be cheaper than SFO > destination.

Thank you for all your suggestions! I will keep researching.

Nonstop flights SFO to TYO have been high for at least 6-8 months and I am not sure why. Typically they were in the $800-$1200 range for many years. Might be due to the decline in the use of hubs with less 747 traffic and the use of smaller planes but this is just speculation on my part.