Especially when you leave from France in '43
Numerous threads on this before, but it's a tough one to search for.
If there's a decent chance of an air patrol finding me, then I will rarely go above 256 or 512. If there's a good chance (Biscay, Gibraltar, Near the Isles at all), I don't go above 128.
Problem is, if you go above 128, as has been mentioned before, the computer takes 1 tick to react to the warning, and the time elapsed is huge in that 1 tick. At 512, thats almost 8 minutes game time your behind. If that's a plane your spotting 8 minutes to, he's probably well into a bombing run, if he hasn't already done one. The math may be off some, but the concept is sound.
If I'm going on a long distance cruise in the middle of nowhere, then higher TC is ok IMO. Going from Europe to the Caribbean is a looooong and boring journey at 128, so I will crank it up into the 1k, 2k range for those trips, sometimes even faster.
If you use SHC, you can adjust what TC the game drops down to when an enemy is detected, I just leave mine at the 1/8 for planes/ships.