Consider the following business rule.

"A customer has a requirement that the Case Tab in the company screen should only display when the Company has an agreed service level agreement and the user accessing the screen is in the 'Customer Service' team."

This is a business rule that can be implemented using the Tab SQL Clause and there are a number of articles that have been written that discuss similar business rules.  

But the rule can also be implemented using the Client Side API.

[code language="javascript"]
crm.ready(function () {
    var slaid = crm.fields("comp_slaid").value();
    var team = CurrentUser.user_primarychannelid;

    if (slaid > 0 && team == 3) {
        //show tab
        crm.showTab('tabnames', 'cases');
    else {
        //hide tab
        crm.hideTab('tabnames', 'cases');