What is the difference in Group Types present in Group Object

Appian comes with a pre-defined Group Type, but you can create your own Group Types from which you can then create Group instances. The key difference is that for the ones that you can make you can add custom attributes. This is useful where you want some data associated with a Group but don't want to implement anything heavyweight (e.g. a database table).

What is the purpose of Custom attributes in Group Types?

Whatever you want to use them for. So, here's a (contrived) example:

Say you have a Team of Claims handlers, each of who has different levels of payment authorisation. You could create one Group called 'Claims Handlers', and within that have 3 Groups: Claims Handlers Level 1, Claims Handlers Level 2, Claims Handlers Level 3. The first group you could make using the default Group Type. The other 3 Groups you could create a Group Type called 'Claims Handlers' and add an attribute called 'Payment Limit' of type Decimal. You could then set this value to different values in each of the 3 Groups of Group Type 'Claims Handlers. In your Application you can now make reference to the Group that a User belongs to and fetch this value to determine whether they are authorised to pay a given Claim.

This would be an alternative design to holding this value in a database table where you'd need to correlate a User in some way to a given row in that table to fetch their payment limit.

Whatever you want to use them for. So, here's a (contrived) example:

Say you have a Team of Claims handlers, each of who has different levels of payment authorisation. You could create one Group called 'Claims Handlers', and within that have 3 Groups: Claims Handlers Level 1, Claims Handlers Level 2, Claims Handlers Level 3. The first group you could make using the default Group Type. The other 3 Groups you could create a Group Type called 'Claims Handlers' and add an attribute called 'Payment Limit' of type Decimal. You could then set this value to different values in each of the 3 Groups of Group Type 'Claims Handlers. In your Application you can now make reference to the Group that a User belongs to and fetch this value to determine whether they are authorised to pay a given Claim.

This would be an alternative design to holding this value in a database table where you'd need to correlate a User in some way to a given row in that table to fetch their payment limit.

Stewart Burchell said:

In your Application you can now make reference to the Group that a User belongs to and fetch this value to determine whether they are authorised to pay a given Claim.

How can I fetch the attribute value in my application?

Use the getgroupattribute() function:

What could be the possible use cases of group types in Appian?

one thing i know ,it's gonna help us setting Security for Schema.https://docs.appian.com/suite/help/23.4/appian-cloud-database-administration.html#group-type-assignment-for-read-or-write-privileges

You could create specific types of groups and add additional parameters to store values together with the group. Then use these values to e.g. control process flow.