Pulling out processes/servers/cables is an ideal way to test what happens when you pull out processes/servers/cables. Especially when you want to see how it affects a system that is too large to realistically reproduce in a test rig (though presumably you would still want to run it in your scaled down test rig too).

Throttling CPU/disc/network is all well and fine and necessary too, but that's only one set of failure scenarios, and won't protect you against a whole range of failures related to systems just disappearing as they crash, or failing to restart, or any number of other concerns.