The size of the Cloudflare network is quite impressive, and in theory this gives Cloudflare customers lightning fast speed.
However, a problem with an ever-growing network is the increased likelihood of a cache MISS for small to modest websites. After all, the more data centers there are, the greater the likelihood that a particular requested file is not cached in the visitor’s region.
An origin shield will help with that. For the bigger websites, an origin shield will also prevent a spike of traffic at the origin server after a cache purge.
(Since an origin shield requires more storage on Cloudflare’s end, I’m totally onboard with making this a feature for paying customers only.)