Using "so..." at the end is sort of like that Seinfeld episode where they end their stories with "Yadda. yadda.."(I think that's it).

There's a few uses

so... you already know the rest

so... I don't think you really want to hear the rest or I don't want to tell you

so... You're not listening to me are you

Which reminds me of the guy that asks you a question then starts randomly going "yeah" "mmm-hmm" Even in the middle of sentences. So I'd trail off and stop talking then after a minute or two he'd ask me something to keep me going or ask me to continue. But you're not even listening, lol. Was an old co-worker and one of the worst lunch times.