Originally Posted by PewterTA
I would disagree. Despite the fact that android has memory management built in, that memory is still finite. I don't wont to have to install more apps than needed as it will eventually hinder performance.
That isn't true though. Although memory is finite, unused memory is useless. If the memory were to get close to being too full, the OS kills off inactive apps. I repeat that users should not worry about how much memory is used, it is not a relevant factor in Android performance. Android manages memory in a completely different way to Windows.
electricpete raised a slightly different point. If an app is actively running, that will have some effect on performance but there is no way that an SMS blocking app would ever consume enough processor time to make a noticeable difference unless it were completely broken.
Having lots of memory in use or lots of apps installed and running will not have any impact on performance unless the app is something like a game that consumes huge resources or is completely broken.
To answer your question about the carrier SMS blocker, it will fundamentally work exactly the same as a third party app. Until a message arrives, it will do nothing. It will briefly spring into action when one does, delete it if appropriate and then go back to sleep again consuming no resources except for a tiny and irrelevant bit of memory that the OS will free up in the unlikely event that it is needed.