Working in a group requires a kind of discipline from people, which some are not used to. I remember to a colleague, who always complained about his office mate who used to shout at the phone, even in normal talks. If people work together and share ressources, everyone expects to be cooperative and not to trash the work and morale of their team members.
The same applies to applications; if they share ressources (because they may run on the same machine), they should release the ressources if they are no longer needed, and should only claim ressources, if they’re needed at all. Consuming all CPU because “the developer was to lazy to develop a decent algorithm and just choose the brute-force solution” isn’t considered a good behaviour. It’s even harder if these applications are contained within one process, so a process crash not only affects application A, but also B and C. And then it doesn’t matter, that these are well-thought and perfectly developed.
So if you plan to deploy more than one appliction to a single CQ instance, you should take care, that the developers were aware of this condition and they had it in their mind. Because the application does no longer control the heap usage on its own (on top of the heap consumption of CQ itself), but must share it with other applications. It must be programmed with stability and robustness in mind, because unknown structures and services may change assumptions about timing and sizes. And yes, a restart also affects the others. So restarting because of application problems isn’t a good thing.
In general an application should never require a restart of the whole JVM; only when it comes to necessary changes to JVM parameters, it should be allowed. But all other application specific settings should be changable through special configuration templates which are evaluated during runtime, so changes are picked up immediately. This even reduces the amount of work for the system administrator, because changing such values can be delegated to special users using the ACL mechanism.