You often only forget once not to remove your disc brake lock from your brake disc, but that one time can be expensive. A disc brake lock is very easy, small and quick to use. A disc brake lock ensures that your front wheel cannot turn any further because it has a solid block of steel.
You can imagine what happens when you start the engine, want to accelerate quickly and then find out that your disc brake lock is still on your disc. All kinds of nasty things can happen from a rollover to breaking down your entire brake system. A lock reminder is a striking cord that you tension between your disc brake lock and clutch as a memory aid, this way you can never forget that your disc brake lock is still on your brake disc.