The other reason is if you need analog analog video output. The Roku 1 is now the cheapest box with legacy analog connections, so it will work an older TV that has a composite video input (i.e., the yellow video port.)
Otherwise, the Streaming Stick looks to be a superior product in just about every way, especially if you're ever tempted to grab your Roku and bring it to a secondary location, like a relative's house.
Roku boxes compared
For a deep dive on the full Roku experience, check out CNET's full review of the Roku 3. Below is a breakdown of Roku's full product line.
Roku 1 ($50): 1080p video; HDMI and analog video outputs.
Roku Streaming Stick (2014) ($50): smaller form factor, adds RF remote and dual-band wireless, YouTube support out-of-the-box.
Roku 2 ($80): adds Wi-Fi Direct remote with headphone jack, YouTube coming later this year.
Roku 3 ($100): adds dual-core processor, motion control remote, Ethernet jack, USB port, SD card slot; no analog video jacks; YouTube currently supported.