Matter level rate cards are typically used when there is an agreement between the client and the firm to work on a given matter for a discounted rate, rather than the default rate for the timekeeper. Matter level rate cards are completely optional. It is at the client's discretion whether they'd like the firm to have the ability to submit matter level rate cards.
Clients can disable the setting to prevent firms from submitting a matter level rate card in Lawtrac. The setting can be disabled under:
My Lawtrac > Application Administration > Firms & Vendors > Rate Card Settings > Turn Off the 'Enable Matter Level Rate Card' setting