Tim, these forms don't come with any explanation of the purpose but I can tell you what I have observed.
It appears that every staffed station on the Milwaukee filled out these daily reports and submitted them monthly to the Division Freight and Passenger Agent. Sometimes agents at low volume stations submitted a months worth of information on one form, as seen here for Enumclaw. I've also seen monthly packets of daily forms where every form was filled out as 'blank'. There was one report for cars received and one for cars forwarded.
At the division level, I've seen reports on various commodities like eggs and autos that may have been derived from these monthly reports of daily activity.
I've been working with these documents as a volunteer with Cascade Rail Foundation. We have boxes full of these forms and we've been putting each month into a labeled folder so we can get them organized and inventoried. They date mostly from the 1920s - 1930s and are mostly from stations south of Tacoma, WA, though there are some from other stations in Washington.
Whatever their purpose, these forms provide some interesting information about what was being shipped where and sometimes the routes the shipments used to get there.
Thanks Ed, for providing the details about UP 175288.
If anyone is interested in helping process this collection of forms, we meet during the day at Pacific Northwest Railroad Archive in Burien, WA, typically on the second and fourth Fridays each month.