Questioner is a vital component to your server if you use a Towny version older than

Questioner’s role is to prompt players when they are invited to a town, and town’s mayors when they are invited to a nation, whether they would like to join the town or nation.

The prompt displays which town or nation is inviting the player and asks for an /accept or /deny response.

If you have using_economy: true in your config.yml then you need to use Questioner. There is one big, nightmare scenario which can occur if you do not use Questioner:

As an example, lets use Miner Steve. Miner Steve could be the mayor of a town or he could be the leader of a nation. Miner Steve invites a resident or town into his town or nation.
Because the server does not have Questioner enabled the resident or town is not prompted about whether they want to join, they are just added.
Miner Steve is feeling devious so he sets his town’s tax or nation’s tax incredibly high! When the next “Towny Day” rolls around, all the residents/towns in Steve’s town/nation are charged the immense tax, bankrupting them instantly! This can also lead to deleted towns.

Questioner is available in the Towny Advanced Release Packages and also for download here: Questioner.jar