From what I’ve seen if you’re using only sunlight and skylight, in order to have proper indirect lighting inside an apartment for example, you should increase the Indirect light intensity on the light itself, but that for me seems to be the main problem with light leaks, so I usually stick with bounce cards.
The bounce card technique is used widely on Max/Maya/Vray/other renderer because it gives better results and you can control much better the indirect lighting on an area.
I also use a bit of boost on the lightmass settings to increase the overall brightness on the scene…but also using the post process Indirect lighting gives you good results ( in realtime, which is nice ).