If a coin is purely deflationary you will later on run into trouble regarding the functionality of the economics. Nobody will use it to transact because holding and only holding is the holy grail. If that is the case and everyone's best decision is to hold, who is going to use it and for what? You need to have a way out for that problem unless you don't care and just try to sell first.
Some people think that burning some percent of coins from every transaction will add value to their coin because supply is reducing. But think like an investor's perspective. Will you invest such a coin where you will lose money in every transaction? what are the benefits of it in long term. If a project thinks that it has too much coin in circulation then it needed then just burn some of it. Why investors will do that by burning their own money!