I shall give a few illustrations which are, however, imaginary.
1. An Advocate gives a Legal Notice. The Party remains silent. Based on this silence, the Court can't give a Decree. Summons will be sent. Case will be heard ex parte if the Party doesn't turn up. And Decree wiil be passed relying on evidence, not on the silence. Defendant has, because he was silent, to bear the costs. If he replies and gives consent to the Advocate, no costs. If the Plaintiff institutes a Suit without sending a Notice and if the Defendant admits, no costs.
2. Court sends a Summons. The Defendant doesn't turn up. This doesn't mean the averments in the Plaint can be taken for granted. The case is decided on merits without considering the silence as consent. In the summons it's written that case will be heard ex parte. Decree can't be given without hearing. It can't be given neglecting evidence. Non-reply to the Summons doesn't go in favour of the Plaintiff. The strength of evidence does.
3. Notice is given to a Public servant. If he reconciles, well and good. If he doesn't, he can fight the Suit. His silence won't be an impediment. It doesn't amount to Admission.