Since my Access days, I've believed in renaming important* controls in reports. Now that I use Reporting Services daily, this practice still holds: ambiguous names like "Textbox1" or "Textbox112" become "ReportName" or "FinalBalance", "table1" becomes "WidgetSalesTable", and "chart1" becomes "MonthlyTrendChart".
As well as better organising the report while in development and adding only a small amount of time to actually do, renaming controls is useful to me later when I'm maintaining a report as I can see which controls contain which data points.
There's one further advantage to renaming controls in a Reporting Services report: because reports are stored in XML format,...