Originally Posted by
dynaryder
No.
^^This. You lock your bike to the same rack every day. You leave your U lock there. Now one day you go to lock up and find someone has filled the keyhole with superglue. Now what? Do you just leave the bike unlocked on the rack? It's now an easy mark. Or what if someone thinks your lock is their's and accidently breaks their key off in it trying to unlock it? Again,you're now without a lock. What if you want to stop at the store on the way home? Plus,leaving your lock out in the elements 24/7 is going to cause corrosion problems.
Not sure why it took PaulRivers response to remember but most of what you are saying would apply to long term rented bike lockers also. Yes they are more secure in theory compared to a ulock someone could fill one of those with superglue, intentionally or acidently break off a key or something else rendering it unusable. It is also has problems with the elements as I found through experience and I had to make sure to carry graphite because my bike locker would stick sometimes in the new england winter.
Carrying an extra lock might help but if you were cased no matter what lock you carried it'll be gone before you get back so I guess you turn around go home and find another way?