Line of business restrictions don't replace security level restrictions; they further restrict user access. You will be able to see everything your security level permits you to see, as long as it is in one of your lines of business.
EXAMPLE Anna is associated with the IT > Managed Services line of business. Her security level gives her View access to "All" tickets. She can view all tickets where she is a primary or secondary resource, even if they are not in her line of business, plus all tickets that are associated with her line of business, plus tickets that are not associated with a line of business. She cannot see tickets that are in a line of business she is not associated with.
NOTE This means that your company can continue to use the same security level for users with and without line of business restrictions, and for users associated with different lines of business.