Microsoft
MicrosoftHello Rajkumar,
I agree, in your scenario using the full LCU may be a better fit. If WAN bandwidth is the most important, and you have a lot of machines in each branch office, then the full LCU may be the best way to optimize your bandwidth. On the other hand, if you have a branch with only a couple machines it may be best to enable Express on a WSUS at your headquarters and then have the machines at the branch download express updates from it. (3 machines x 150mb is smaller than downloading a full LCU to that small branch, and of course you wouldn't need to maintain a WSUS server there)
Yes, you should be able to clean up the express content library (assuming your devices are only on win10 where updates are cumulative). If you still have some win7 or win8.1 devices you may not want to clean out their older updates since they aren't fully cumulative from RTM. As long as you keep the latest cumulative express update, cleaning up the older ones shouldn't impact download bandwidth at all.
Unfortunately I'm not an expert on the SCCM client. I'll reach out to some of my colleagues to get an answer on the local disk space. The Windows Update agent keeps updates around on the disk until they've been superseded for 30 days. Which generally means you have N-2 worth of updates on the disk and then they automatically get purged. I'll ask the SCCM folks if they have a similar design.
Mike