First, I do not think being a deflationary token is enough reason to invest in any project, there have to be other good reasons which must prove why the project is worthy enough to be invested in. Although there was a time the trend or rather hype was much about deflationary tokens, because the team made it look like, by having small supply which will reduce overtime, then the price of the token will keep increasing, this idea was used to create many scam projects, until it became clear that without good use case, being a deflationary is nothing. In the same way, another purpose of having deflationary token is this, when a coin supply is much and the team aims to reduce it as time goes by, they can implement deflationary features or burn features, thus for every transaction the supply keeps reducing.