Activating Package Checks in a Running System

Does anyone have experience with the activation of package checks in an ABAP customer system already in operation for years and with a large code base?

I’ve been playing around with RESTRICTED mode and I like the features provided by the encapsulation, mainly the aspect revealed via package checks that standard SAP objects should not be just reused mindlessly.

Do I have to fear that once activated it will cause problems in existing custom objects, as nobody payed attention to package interfaces before? I’ve seen an error popup during DDIC activation on violation, but it seemingly can be bypassed. I tried to search on parameter DEFAULT_SEVERITY in table PAKPARAM and how to use it, but without any success.

PS: I’m also interested in any experience with package checks in customer systems. Does it worth it in the long run?