I've flashed my TP (lots) because I am a geek and like messing/tweaking via the registry. If all my preferred customizations are cooked in or UC'd I can always hard reset instead of spending hours getting back to square one.
More to your question: I flashed my son's TP because his line has no data plan and the stock rom kept driving him crazy with notifications.
I wasn't able to flush all the data related apps that were causing probs for him without cooking up a rom without them. He also complained that the TP seemed slow compared to his old phone. Subjectively, he finds the new rom much snappier and cleaner.