The entry in startup is for updates, it checks for updates, every so often.
It can be disabled / deleted in startup
But if you do use it, you'll have to go to the oracle/sun site to check for updates when they come out.
And every time you update it you SHOULD uninstall older versions, which can be full of vulnerabilities. If you dont uninstall older versions, you can be hit by whatever vulnerabilities are in that version of Java
I dont use it. I dont have any programs, that need / require it.
Some sites and programs MAY need it. In order to work. No Java it wont run or work properly