Example

Once Group watch is enabled tiki wide by an admin ("Settings > Control Panels > User Settings > Group watches"), a few new icons will show up to the right of the previous ones in tiki objects, like in the example below of a tiki forum.

Once the admin clicks on those new icons, he/she will be able to set which groups have to receive emails:

If a user has both a user watch and a or n group watches on the event - he will receive one mail only

There is no way for a user to unsubscribe to this watch.
Note that it is possible for a user to quit and join a group if you set a Wiki page with the SubscribeGroup plugin.

Group alert vs Group watch

Both features are fairly similar - two different developments done almost at the same time.

Difference:

group alert is more resource consuming as it searchs all the groups for each access - group watch is not if not used
group alert has an option to select some users in the groups - group watch does not have.
group watch can be seen in the notification panel . It doesn't seem that a user cannot have a global view of group alert.

Tiki Features supporting Group Watches

Blog
Categories
Calendars
Comments
Image galleries
File galleries
Forums
Tracker item
Wiki

Group watch of categories
This will permit an admin to have a whole group informed of any change in a category. This is very useful for project management or a Document Workflow

Group watch of calendars

You need to set just one calendar as visible, from the list of calendars you may have in your tiki site (if you have more than one), in order to expose the links to the feature to monitor ("User Watch") or group monitor ("Group Watch") that specific calendar.

Alias
Group watch \| groupwatch \| GroupWatch \| Group Monitor

Group Watches
An admin can add one or n groups - each user of the group (member at the moment of the notification) will receive a mail when some changes occur to this tiki object.