Not necessarily. As mentioned, YACB does have a database of known scam numbers and it downloads updates periodically.
Anything else that comes in you manually blacklist. Wildcards are accepted which is cool. Note all the Radius-labeled calls below.
Also, when set as the default phone app it will catch and block before the phone gets a chance to ring. It does not impact normal functions of call management. What’s not blocked comes through normally.
Regarding that, some dialers like Simple Dialer will “nag” if it’s not the default handler. On GitHub, a user who uses YACB as the default, asked if that behavior could be an option that can be turned off. The dev was dismissive, IMO, saying what’s the point of the dialer if it’s not the default. I added my two cents but it probably won’t matter.
I just got a call from a number I want to block for the future and now I wonder whether there´s any issue with the built in call blocking feature of eOS phone app or why (for what usecase) would one need an extra app for blocking numbers?
edit: now that I think about it I understand that an app might make use of a database to enable “block in advance” (or the like)