Pros
Once offered a permanent position pretty good bet job will be there, never heard of layoffs. I worked in a smaller office in a smaller community so the co-workes were real nice as were most of the town people. You need to enjoy people to work with the community because it is more than just working with the 'public'. People relay on the postal service for more than just mail, in a smaller town it is the hub of what it occurring in the town, people would gather at the PO to chit chat about family, friends or issues within the community. As a windoe clerk it was not unusual to be placed in the role of listener to issues in folks lives.
Cons
if you deliver mail the weather is always to be dealt with, need to be a people person. The waves of mail would be overwhelming at times. One day you would come into work and see 4 trays of mail ( a tray is 2ft of letters placed back to back in a tray)for you to sort and deliver, the next day it could be 20 ft plus the magazines (flats) and newspapers and circulars. As a letter carrier these days were heavy to carry and did take longer. If you are the carrier to take over on the regular carriers day off it will take you much longer to sort & deliver the mail becuase it does take awhile to build up speed at "casing' mail.