Therefore, sabbaticals are beneficial both for employers and employees.
1) both...and...引导的两部分应该并列，因此，employees之前是否省略了for? 即不省略的状况下应为：beneficial both for the employers and for employees?
2) beneficial both for employers and employees 是不是可改为：beneficial for both employers and employees.
你的理解是正确的。原句写作比较随意，在正式书面语会被觉得是欠妥的。应为both for A and for B, 或者for bothA and B.