Generally speaking I advocate having automatic updates enabled which works fine on my main PC (a Win7 quad-core desktop), but my C2D laptop is presenting me with a problem: I only use it when I need to, which isn't that often. That means that WU takes longer to process updates, saturating a core the whole way. I recently tried leaving it constantly running for several hours but it didn't pick up any new updates, and essentially disabling one core on an older dual-core CPU isn't a good thing.
To use it at full speed I ended up disabling the WU service for the time being, but I would very much like to get back to having WU work properly on it. I don't think Win10 is an option as the laptop has Intel series 4 graphics and the Win81 driver didn't work too well with it (graphics corruptions when typing - not serious ones, but off-putting. No newer drivers available). It's running Win7 64 atm, up-to-date as of a few months ago.