Should I defeat the Wrinklers?

Wrinklers reduce the amount of cookies per second that you earn, but when you defeat them they give you more than they took, so it´s probably best to wait for quite long before you defeat them.

The best strategy seems to be to have as many wrinklers as possible and to only defeat one when you need more cookies.

More about the mechanics and maths on how the wrinklers work

There are 4 wrinkler related achievments that require you to defeat 1, 50, or 200 wrinklers and a shadow achievment that requires you to

"Burst the near-extinct shiny wrinkler"

There are also 5 seasonal achievments that you can get by unlocking and buying season based items that you can get by defeating wrinklers during those seasons. One is for halloween and you can get 4 during eastern