iPhone 5C bottom The candy-colored iPhone 5c was one of the most recent phones to come with a 4-inch display. Steve Kovach/Business Insider

If the rumors turn out to be true, Apple will unveil a new, 4-inch iPhone on March 21.

To many, this may seem like a strange decision. After all, the last iPhones that had a 4-inch display were the iPhone 5C and iPhone 5S, both of which are two and a half years old.

Plus, the larger-screened iPhone 6 and 6 Plus models (and the more recent "S" variants) sold in record numbers.

But Jan Dawson, an independent analyst at Jackdaw Research who also blogs at a tech industry opinion site called Techpinions, thinks there are two good reasons for Apple to bring back the small-screened phone.

1. It may boost sales during what's usually a relatively quiet period for Apple.

The spring and summer months are usually *relatively* quiet in terms of iPhone sales. ("Relatively" has to be taken with a grain of salt, as Apple sells way more premium smartphones than anyone else.)

"Q2 and Q3 sales are typically off by about a third from sales in Q4 and about 25% from sales in Q1," Dawson writes, "So boosting sales in this quarter would help even out the seasonal variability."

Apple usually debuts its new iPhones in September, so some people hold out in the spring and summer months waiting for the newest device to come out in the fall. Dawson thinks that Apple may have found that the iPhone 5c, which was a less expensive alternative to the flagship iPhone, sold well even in the off months because "the kind of people interested in a 5c were not those who needed the latest and greatest device as soon as it was available."

This chart, courtesy of BI Intelligence, shows how iPhone sales vary from season to season:

bii apple iphone unit sales yoy growth BI Intelligence

2. It'll give the tens of millions of people who still have 4-inch iPhone a brand new model.

Dawson estimates that there are between 200 and 250 million people who still use iPhones with 4-inch screens. For a variety of reasons, they haven't felt the need to upgrade to a newer phone.

Perhaps they like the size of the 4-inch iPhone, and, as my colleague Steve Kovach recently found, how it fits in their pocket and how they can use it with one hand. Or perhaps a newer iPhone is too expensive. Or maybe they just don't need it yet!

It doesn't matter why these millions of people haven't upgraded yet, all that matters is that they have an option for a new phone that's the same size as their old one.

"...what’s happened is many of those owners of smaller iPhones have simply stuck with them, which has also dampened iPhone sales over the last year and a half," Dawson writes. "By introducing a new 4-inch phone, Apple is giving those customers a reason to upgrade."

Be sure to read Dawson's entire column, which includes speculation about the price of the new phone, at Techpinions.

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