I prefer to have as much info in ProSeries as possible, as opposed to tracking it offline in a spreadsheet in order to split it out manually.  What I envisioned in using the 1098 worksheet was that that would allow me to enter the data in once and the program would allocate it based on the percentages I set in the Sch E.  That is what I thought the "allocate personal use items to Schedule A" checkbox would do for me.  If that in no way affects the Sch A, then I'm not sure why they entitled it as they did.