Callsign,
Remember most airlines have more than one type of aircraft. Everytime you transition from one type to another you will undergo line training. Also if you upgrade to the left seat you would then fly with a line training Captain or Check airman as they are called in the US.
As previously mentioned, most airlines procedures are similar but company data like operations manuals, weight and balance forms, runway analysis books, quick reference handbooks, performance charts and TOLD cards etc may be presented differently.
The most challenging line training you will do is in your first airline job. After that it's pretty much more of the same, kinda.
AL