Using work computer for personal stuff ?

I know people say employers can see what I look at if they want to view it. But what if I don't care? Lol. Is there another reason I shouldn't use the work computer to check my email ? Social media? Etc

*to clarify, I am referring to after work hours and / or lunch time. My laptop crapped out so I'd rather just use theirs vs buy my own unless there's good reason I shouldn't?