Can go to events and Holidays, catch a vistor or item you missed earlier.
Neighbors don't go away.
Weeds don't appear.
Can't use money cheats (Aka Skipping to 2099 with 50,00 Bells in the Machine)
Has to face weeds if coming forward (Unless you tile the whole town )
Can use money cheats from Wild World
Can skip to Holidays and visitors
If you want to catch rare bugs/fish.
May lose neighbors
Weed invaded town(Unless using the Tiles)
Lost cat and Blanca doesn't happen
The Raffrisa with Flies appear until you remove every last weed.
This also works for Wild World!