Is SCCM/MECM smart enough to simply know that the computer doesn't need it?
Yes, but it's not up to ConfigMgr specifically. Updates have applicability rules and based on these, which the Windows Update client evaluates (in the form of compliance scanning), the ConfigMgr agent determines whether or to download and install specific updates deployed to the system. These applicability rules are defined by the creator of the update catalog.
In general though, you should try to narrow down the targeting of non-universal updates as compliance scanning has overhead. This overhead managbale and non-crippling in most cases but that still doesn't mean you just want to deploy everything at all devices.