Even though there's a perfectly good bridge right there:
[The ford in a shot I took a couple of winters ago]
Basically my motivation is to get my feet used to running while they are soaked. Summer or winter, doesn't matter: in the summer, it's a refreshing cool-down. In the winter, it's toughening process to run with cold, wet feet...which, by the way, quickly drain and warm back up within a couple miles.
See, in a race or a backcountry training run, you need to be prepared for an array of conditions which you may face, to include stream crossings. Doing crossings deliberately in training gets you used to do it and running afterwards with wet feet. And it crosses another variable off of unfamiliar things that could help derail you--mentally or physically--in a race.
I have found for me that running with wet feet is no more likely to produce blisters tha running in perfectly dry foot gear.
FOOTNOTE. The route, for you anal-retentive types (like me):
For my place here are the details: I usually head down Angle Road, right on the Clay Hill-Kauffman Road, across U.S. Rt 11 on Kauffman Road West, right onto Guitner Road, right on Coontown Road, right on Gomer Road, right on Miller Road, ford the Conococheague here, right on Frederick's Mill Road, across U.S. Rt 11 to old Rt 11 (Main Street in Marion), left onto Colorado Street, right onto Angle Road, which I then follow south back to the house.