Dreamhost's 'unlimited' resource allocations are attractive but they fail to give guidance about how much is 'reasonable'.
For example, consider disk usage. In the normal course of website management, garbage accumulates on disk, and the question arises, how often to do garbage collection.
Every day? Every month? Every year? Obviously, the answer depends on how much garbage there is. But in terms of a precise numerical guideline, the answer is not obvious.
Automatic garbage-collection at too-frequent intervals could waste more resources in processor time and disk-head erosion than it would gain in disk-space.
The closest equivalent host to Dreamhost that I've been able to find (similar price, similar technical orientation) not offering 'unlimited' resource usage allows 100GB disk usage on its basic shared hosting plan.
This seems to suggest that it is reasonable to allow total disk usage on a Dreamhost account to accumulate to up to about 100GB before worrying about how to garbage-collect it.