"What are the consequences of taking a 20-day continuous leave when we have a leave balance?"

It can range from “nobody cares” to “who the hell will meet client timelines”. Your answer lies somewhere in-between.

I mean you can take such a leave, assuming your leave is approved. Even if it is approved, you have timelines to adhere to.. Emails which need to be replied. When you come back, it will be hell. In fact, for anything more than 5-6 days of consecutive leave, it's difficult to catch up. Note, it can be managed in case you're getting married or you need it for a medical emergency. In such a case, your work will be assigned to someone else or will be planned around your absence

Have a discussion with your lead and manager atleast 1-2 weeks prior to your leave, so that they can reassign any current / upcoming tasks to others and schedule work accordingly.