To-day, I have come across for another important reason to be able to display aggregate bets in the matched/unmatched window:
I use Betfair mainly to lay bets I placed externally (at the bookies). Sometimes, I lay multiple selections because I backed these at different bookies. For instance, to-day I laid two external bets and backed a third selection.
In that scenario the P&L shown for the selection under its name is meaningless because I am not interested in the combined liabilities. What I need to see at a glance is the total liability for one selection. This acts a sanity check for me because I can work out in my head whether the figures look about right.
To-day, after having placed several small lays at different odds in-running (in addition to other bets in the same market), the bets didn't fit in the window and there was no time for scrolling and adding up manually. I had no idea whether I might have overlaid.