What does it do?
The Waiver clause allows a party to strictly enforce its rights in terms of an agreement even if it has been lenient in the past, in other words, it confirms that leniency does not result in a waiver of its rights. This is because a party may not always want to enforce all its rights under an agreement at a point in time but do not want to lose the right to do so later.
Real life example:
Llewellyn rents an apartment to his friend Tim. Their rental agreement states that the rental must be paid on or before the 25th of the month. Tim pays late occasionally, usually around the 1st or 2nd of the month. Llewellyn overlooks this and does not mention it. Having a waiver clause in the agreement means that because Llewellyn has been lenient does not mean he cannot strictly enforce his right to payment on or before the 25th in the future or use any of the remedies in the agreement as a result of this breach by Tim.
Kleva Contracts sample wording:
No waiver will constitute a waiver of rights in respect of any later breach of the same or any other provision