I usually send PMs especially if I would to ask any personal nor sensitive messages through telegram. I haven't tried using encryption methods like the others have commented, but telegram, for me, is enough of the safety. And with bitcointalk PMs, once a user tried to contact you  and you think the conversation would take longer and must be secured, better take it on Telegram. But if you would simply tell them a long single message that contain some sensitive information but you're choice is PM, then better follow other's suggestion.