Jailing would be a great thing IF:
- it was really secure; but it's not, in fact there are many potential workarounds
- it was stable; but it's not, it's often difficult to setup and can occasionally bring some problems difficult to find; also, people often forget to update the chrooted libraries, making it *much, much less* secure than a normal setup
If you don't require very high security standards (and therefore have an higher security budget), it's probably time wasted in exchange of the little security it adds.