Why are some fields disabled in "Bulk Edit"?

The "Bulk Edit" feature is a really nice thing in MS CRM. You can edit multiple records at one time. This was already described on number of other blogs.

However, there is a very common question "Why are some fields disabled when I use 'Bulk Edit'?" although they are enabled on the form? The answer is: each field that has an event enabled will be disabled in 'Bulk Edit' . Even if there is no client side script attached - it is enough that the event is enabled.

There is a rationale for this - what should happen when a script should be run on OnChange event when several records are edited?...