Index check restrictions and effects for Data Columns

Content (please ensure you mask any confidential information):

I have the following questions.

Quote Process>Data Columns
We have added several Transaction attributes to the above.

Each setting has an Index checkbox, but if you turn on some of them, the remaining checkboxes will be deactivated and you will not be able to turn them on.

So, I would like to check the following:
1.Where can I check the restrictions on what indexes can be turned on?
2.What are the functions of Index and Keyword Search Enabled? I would like to know if there are any issues when turning them off.