I use a lot of varchar columns in mySQL. One of the things that I always run into is how much varchar to allocate? After all, you don't want to be wasting space right? So I always try to estimate it as close to the lower bound as possible?
I've learned now is to always try to overestimate. And then overestimate some more. I've never had a time where making I needed to shrink the size of the varchar. I've only encountered scenario's where I had to change the varchar to something bigger.
And it's horrible when that happens. It's painful and bad. In the case of what happened to me recently... I lost data because mySQL truncates your shit without warning. I know that postgres will at least throw an exception so that you know. Either way, you're going to be losing data.
It reminds me of the youtube gangnum style video where the guy used an integer for the counter thinking a video couldn't possible reach it. Regarding that... I don't know why he didn't use an unsigned integer. I digress.
tl;dr - always go for the bigger var char. Don't preemptively optimize. Make it 3x bigger than what you think. You never know what crazy customers / you will want to do in the future