You Might Pay More for Certain Types of Data
If your ISP or cellular carrier offers certain “zero-rated” services, you’ll definitely want to avoid using Private Relay for these, as they’ll end up counting against your data allotment.
For example, if a carrier offers free access to stream music from Spotify, it can only do this by analyzing the traffic that passes through its servers. When it recognizes Spotify traffic, it excludes that from normal data charges.
In this scenario, however, since Private Relay hides all your browsing traffic from your ISP or carrier, it can’t exempt Spotify traffic, so this will encounter data charges in the same way as any other traffic.
The good news is that since Private Relay only works with Safari, zero-rated services that work through dedicated apps should still be fine — this traffic won’t be hidden from your ISP or carrier — but you’ll definitely want to avoid using these services in Safari when Private Relay is enabled.
It’s also worth noting that Private Relay can be disabled on a per-connection basis, so you could switch it off for your Cellular Data connection while still leaving it active on your home Wi-Fi network.