A limited release is usually a way to combine minimum financial risks with some maximum "bush telegraph" effect.
Limited theatrical release is a film distribution strategy of releasing a new film in a few theaters across a country, typically art house theaters in major metropolitan markets. The purpose is often used to gauge the appeal of specialty films, like documentaries, independent films and art films.
Now, according to the American Film Market:
For many independent filmmakers, whether or not their film reaches the big screen means everything. No matter the money to be made via television deals or the massive audiences possible with VOD, a theatrical release is where it's at. Seeing a film played in a theater is still regarded as the best way to experience the art form. It's also, understandably, the goal of many film producers. By looking at a complete set of films made in a single year, we can see how likely it is that a given film will realize that dream, and it turns out that there's actually a pretty good chance a film will play to a paying audience at some point, if that's what the film-maker sets out to do.
However, the numbers say that an independent film will, five times out of six, not go on to make much money in theaters. Knowing how to maximize revenue from the home market remains an essential skill for an independent producer.
There are also other reasons (even if they don't seem to apply in your case):
A common practice by film studios is to give highly anticipated and critically acclaimed films a limited release on or before December 31 in Los Angeles County, California, to qualify for Academy Award nominations (as by its rules). Highly anticipated documentaries also receive limited releases at the same time in New York City, as the rules for the Academy Award for Best Documentary Feature mandate releases in both locations. The films are almost always released to a wider audience in January or February of the following year.
So, no matter how many theaters there are, the number by itself seems to be more of a marketing issue than just some artistic choice. If you want something people will talk about or fight for, make it rare. That's one technic. If you want to minimize the risk of losing money, do the same: a small number of theaters. Combine marketing technics when needed.
More to read: Why Are Limited Release Movies Still A Distribution Method? -- Film distribution -- film distribution strategies (from legal POV)