For example, I tend to begin making sketches of tracks often using the same key, because it's comfortable and familiar. But what if I put these tracks together, on an EP for instance and each track is in the key of Am. Let's also say they begin and end on that key.
It seems to me, although this is just a thought experiment. That although each track might be great by itself, and with lots of variation within the track etc. The album's effect on the listener as a whole would be a lot more interesting if the key of each proceeding song was different, or the beginning chord of the next track would be a logical progression from the last. The different key/chord could even be used to create tension, dissonance.
Hope this makes sense
as I say I've only been thinking about this and haven't put it into practice, or studied any commercial albums. It seems like such a basic thing and yet I can't seem to find any theory/info about it.