contract assets

Hello,
I’m confused about the section on contract assets (IFRS 15) in my text book. I’m not sure when it would be appropriate to account in that way as opposed to just recognising revenue as performance obligations are satisfied. Would it be right to assume that contract assets are recognised when an entity is creating an asset that would be capitalised in its own books if it were for its own use? & so a contract asset has to be recognised instead? Rather than eg a phone contract where the resource the entity uses to fulfil its obligations would be expensed.
I understand the principles of revenue recognition generally but this confuses me, I would really appreciate your input.
thank you