The big benefit becomes clearer when looking at a collector's collection, swap list or wish list. It's then very easy to know how many items the collector has of each country, company or even series.
Here's for example the information for an expert collector on Colnect, Dravec
Phonecards
Collection: 7,546 Phonecards
Swap list: 1,290 Phonecards (Match with my wish list)
Wish list: 6,199 Phonecards (Match with my swap list)
Stamps
Collection: 1,137 Stamps
Swap list: 3 Stamps (Match with my wish list)
Wish list: 5,678 Stamps (Match with my swap list)
Coins
Collection: 2,155 Coins
Swap list: 301 Coins (Match with my wish list)
Wish list: 10,938 Coins (Match with my swap list)
On the back end side of Colnect, the system is very flexible in supplying the given information so the real challenge was to try and create an as-intuitive-as-possible user interface. I've recently made a post about usability and the addition of counters and simplification of the user interface that followed is a big step forward.