I have a standalone Windows XP SP 2 configured with 2 HDs (giving about .5 Tbytes of storage) and 1GB of RAM. Drive partitions are normally labeled C through L (different programs and topics for different drives). It is fully patched and auto update is on, and Windows Defender also auto updates. There is anti virus software which is also updated daily. Office 2007 is also on the machine. Connection to the Internet is via dial up modem with one of several ISPs (sometimes one or another will have a tech problem, so I find having choices when trying to connect to be good). I use Port Explorer to keep track of what is happening on different ports when on line, and Process Guard to control which process runs when. Now to the question..

Several days ago after a reboot when it wanted to start this time I told Windows Based Enterprise System (i.e., WBEM) no. After repeated queries I told Process Guard to remember my answer and now WBEM doesn't try anymore. As stated that was several days ago. The machine seems to continue to behave normally without WBEM. MS Windows Defender still auto updates and so do the other programs. I am still able to defrag and perform other operations with no difficulty. The firewall still seems to be operational. NISTIME can still access the time.

I find a lot of techno gobblegook but not much REAL usable info about WBEM. My summation seems to be a business product that doesn't do much for an at home USER with a single machine. I also note that when it ran, it occasionally used a lot of CPU power (and a service host accessed MS and Akami web sites a lot at odd moments but now no longer do once auto updates finish their tasks).

So anyway, what is WBEM good for from the perspective of a non-LAN machine, and what are the downsides to keeping it off?

I've never heard of a Win XP component called Windows Based Enterprise System, actually I'm fairly certain it isn't something that ships with XP.
When you Google WBEM you get most hits on it being short for Web-Based Enterprise Management.
Microsoft do have an implementation of Web-Based Enterprise Management called WMI that is present in all versions of windows since win 2000. Is it WMI you've blocked?Yup. Going on a week now. Actually according to MS WBEM is merely one component of XPs WMI. My WMI is operating. However, the description of exactly what the WBEM is, why it is needed and how it does it is vague. I am growing INCREASINGLY suspicious of the WBEM falling into the gray zone of the borderline of Spyware. I have experimentally blocked many different DLLs over the years, and normally if I have erred the computer lets me know RIGHT away (i.e., reboots in a loop, can't find C:, firewall won't turn on, modem won't dial, etc.). However with the WBEM dropped the only noticeable effect is less CPU power being utilized (MS Process Explorer tracks that for me), and much fewer connects to MS and Akami. I do know (from an old Lavasoft email) that there was a big industry debate a few years ago as to what was and what was exempt from being labeled Spyware. Enterprise is a word with many definitions. Given that its absence seems to be totally unimportant for my enterprise of running my machine, but the machine establishes connections to Akami and MS when it is on, I can not help but wonder if it's real purpose is to help the business enterprise of the owners of the Windows name (i.e., MS). Now I could be 1,000% wrong as the poorly written techie spiel on the MS website also implies the purpose of WBEM is to enable the machine to better connect to remote components. Now why and how contacting MS or Akami becomes an essential part of that process isn't even mentioned, much less explained. Further it is possible that allowing WBEM to run as part of the WMI does not in and of itself result in the calls to MS and Akami, but that rather a third not yet noticed process is then called when it detects WBEM is running. This last possibility is what inspires my query as to what is known about WBEM and what is it good for?