This pattern is used to emphasize that something is nothing more than what is stated, often to minimize its importance, value, or scale. It can carry a nuance of disappointment, modesty, or realism. For example, if someone praises your skill, you might say it is just a hobby, not a profession. The construction is formal and primarily appears in written Japanese, such as news articles, essays, or formal speeches. In casual conversation, you would rarely use it; instead, you might use ただ~だけ or しか~ない. Note that the pattern typically attaches to the clause that is being downplayed, and the whole phrase often precedes a conclusion or a contrasting statement.