Hello,
it depends on the change you're doing. Since my deployment is based on WAR, which will be exploded by Tomcat, I can modify all the dynamic resources (JS, FTL, CSS) that are not bundled in JARs while the server is running. I / we only bundle Java-classes in JARs and add all other resources in the AMP assembly. This way, we immediately get a report if a business module overrides a default Alfresco file or a file of another module when the AMPs are installed in the WAR via MMT. You don't get that via the JAR way and have to rely on classpath ordering / lookup, which could lead to some files from a module transparently hiding files from another one…
Anyway, only if I modify a Java class or Spring context file (*-context.xml, not server-side JS / FTL) do I have to re-build, re-deploy and re-start the server(s). All others can be edited while the Tomcat is running and I never had to deal with a locked file. I don't use the embedded Jetty via Maven plugin at all…
Regards
Axel