The only way subbing disadvantages if one team is allowed to do it and the other isn't. Both teams are allowed to do it. Why someone who is losing would want to eat time off the clock is not for the ref to decide but they could. In a running clock tournament with unlimited subs it would and has been an effective tool to win. If the ref adds time to compensate then not so much. I get it , traditionally, culturally, soccer is a flowing sport with not a lot of stoppages, but if the rules allow, call it a loophole if you want, the use of stalling tactics to eat time should be allowed. As a ref you don't have to agree with the rule, you simply have to enforce it.