I see this a lot, and I also made the same mistake for a long time, because of the defaults of the ESX installer a lot of people tend to create a partition for /var/log. But keep in mind this means that everything else inside /var will belong to the root file system.
So what’s the problem? Well there’s a possibility that your / fills up with core dumps! Some of you might know this and some of you might not know this, but /var/core is the place were core dumps are stored for the Service Console. So when for some reason it starts generating dumps it can and probably will fill up your root filesystem very quick and thus cause the host to halt. Last time I witnessed this it was caused by a hardware vendor agent.
yes, the dumps for ESX service console are stored in /var/core and its usually better to just have a seperate partition for /var (and /var/log .. if you’re paranoid).
Although the default esx server options are good too, unless you have specific requirements.