For those wondering about a potential Syrian intervention, there is the classic question of coalition of the willing vs. NATO. Sarah Kreps and Patricia Weitsman have books on the question of the relative effectiveness of coalitions vs. alliances and why the US chooses one or the other. Nora Bensahel did some work on this earlier. There is much to say and to study on this topic, but I just want to say one thing:
Choosing coalitions of the willing so that you don't have to deal with caveats (restrictions a country will impose on how their contingent is used) is a mistake because countries in coalitions of the willing also can and do impose restrictions on how their troops are used. Just ask the Americans about all of the caveats imposed upon partners deployed in Iraq in 2003-2007. Yow.
So, if you think going caveat-free is one of the key pro's to relying on a coalition rather than an alliance, think again.