The biggest problem I've seen isn't the estimate itself but the telephone game that happens after. You say "probably 2-3 weeks" to your manager, who tells the PM "about 2 weeks", who tells sales "mid-month", who tells the customer "the 15th".

By the time it reaches the customer, your rough guess with explicit uncertainty has become a hard commitment with legal implications. And when you miss it, the blame flows backward.

What's worked for me: always giving estimates in writing with explicit confidence levels, and insisting that any external date includes at least a week of buffer that I don't know about. That way when the inevitable scope creep or surprise dependency shows up, there's room to absorb it without the fire drill.