There are several advantages: first, \operatorname will produce the proper spacing before and after for an operator, which is slightly different from that for \text in some situations. Second, \operatorname will allow the use of \limits and \nolimits for handling the placement of superscript and subscripts to that they act like \sum. For example, \operatorname{sup}_{x\in X} would put the subscript underneath the "sup" when used in displaystyle. Third, and perhaps most important, \operatorname gives the proper semantics for the usage (where \text gives the wrong semantics), and that can help things like screen readers to better voice the meaning of your expression. So while it is a little longer to type, it is good to get in the habit of using it.