Тут уж is being used in obvious situations, when events happens in such unpleasant succesion, that there are not many options left to say / to act.
Approximately,
Now that you found my letters, containing blackmailing stuff, how can I reject that I am blackmailer?
тут уж [теперь] сказать нечего = что я могу ещё сказать [в этой ситуации]? Да, я шантажировал её!

Example 2:
"Тут уж не до хорошего" we say when the situation is difficult and we are hoping on the chance, that there is a way to minimize negative consequences.
You want to buy a bus ticket with convenient departure time (tomorrow morning for example), but suddenly realize, that many people who are staying in queue before you, will probably buy all tickets, maybe even on all buses departing tomorrow. You are ready to put up with the fact, that you will unlikely get ticket on the convenient bus , and can say: Тут уж не до хорошего, хоть бы на последний автобус билет взять.