If you have an album that has seamless transitions, with one song flowing into the next whether that be the drums that come in at the end of one song being the drums for the next song, or a melody for the next song fading in at the end of another. Is it as easy as just laying/lining up one on top of the other or is there more involved?
I may not be an expert in this topic, but being a dj as well as a producer, I would approach this as a dj. Use the stereo mix to fade in fade out, beat match where possible and don’t be afraid to use effects on the stereo mix. If songs have common instrument that needs to continue, you may need to import one mix session into the other, and hopefully your computer has enough power. I recommend printing the mixes to an audio track as opposed to bouncing offline.