What is a profile?
A profile is a collection of permissions and settings that is instrumental in determining a user’s functional access (apps, tabs, object-level permissions), how information is displayed to the user (page layouts, record types, field-level security), and a wide range of other permissions. Each user must be assigned one profile.
User Interface settings will be expanded upon in detail later in this guide.
What’s the difference between standard and custom profiles?
Standard profiles are included with Salesforce. Object-level and user permissions cannot be changed on these profiles. Standard profiles cannot be deleted.
Custom profiles are created by an administrator and can be fully customized. Custom profiles can be deleted.
When should I create custom profiles?
Generally speaking you’ll want to create custom profiles prior to assigning users to profiles. As you have limited ability to change standard profiles, it is generally a best practice to assign all users (with the exception of the system administrator) to custom profiles.
If users are assigned a standard profile and you later need to change their permissions (e.g. add read access to a custom object), you’d have to create a custom profile and then migrate all of those users to the custom profile.