I don't have Spectrum, so this is all second hand.
In the past I've read you have to have at least one Spectrum box connected on your account, but you could use the Spectrum app on Rokus on other sets without an additional Spectrum box.
According to this article "you do not need a Spectrum cable box now" but it's not clear to me if they are saying you don't need the box at all, or just on the set with the Roku.
Note that Spectrum and Roku are in renewal negotiations at the moment and new Roku Spectrum app installations can not be downloaded until an agreement is reached.
Also note that we see a constant stream of complaints here about problems with the app that Spectrum supplied to Roku.
- Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
- Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T
- TCL Roku TV 43S425/C107X, Ser X000001R60KV, wifi
