In my opinion its useful to remember, in the current hoo-ha, the crusades have been vastly overemphasized in their general importance in European and world history.
Once you had gone over the various Eastern Mediterranean, Spanish, and Northern crusades, you tend to try to look at thematic issues such as the economy, art, architecture, music, law", the development of states, or intercultural relations." And this is where the problems begin.
That does not mean that as phenomena they did not intersect with developments in all these areas, but the were not, in my judgement essential to any given area. I'm far from the first to notice this - Donald Logan in his recent excellent textbook on the Medieval Church makes just the same point.
- The focuses of eastern Mediterranean trade were Constantinople and, above all, Alexandria. Until fairly late on these were not focuses of any crusade, and the crusades were only intermittent episodes in the pulse of trade.
- You may have got some mixing of Byzantine, Armenian and Western Art (Queen Melisende's Psalter, etc.) but there are very small number of such items, and such mixing occurred in Southern Italy as well.
- Intercultural relations: Sicily, Spain, Venice, etc, were all more important.