I believe the beeping is for the blind assist function, in addition to the lights in the exterior mirrors.
The lane keeping function has a camera that looks at the road markings and checks whether you're crossing unintentionally your lane. Technically there are two modes (standard and adaptative). It can also be completely deactivated.The signalling is through vibrations in the driving wheel. The adaptative mode will (in addition to the standard) avoid signalling if you're actively accelerating, braking, steering.
I was wondering whether anyone uses (loves, hates) the function, or deactivates it due to it being too disturbing.
I'm not sure if it's the same, but I tried it on a Lexus once and ended up deactivating it. On the Lexus, if you change lane without indicating, it momentarily corrects the steering and puts you back into the lane you're in. In some ways it's impressive, you can take you hands off the wheel and when the car gets close to the white line it actually alarms and corrects the steering to keep you in your lane. Coupled with the collision avoidance, you could theoretically fall asleep and the car would keep you in your lane and then bring the car safely to a stop when you came to stationary traffic...However, there are often times where indicating to change lanes on a multi-lane carriageway is not required (or even advisable), such as returning to the left lane after passing a slower vehicle. If you do that, the sudden tug on the steering to get you back into your current lane is alarming! I suppose you could get into the habit of always indicating - even when you technically don't need to, but I only had the car for a few days (hire car) and it wasn't long enough to change habits so I disabled it.
The GLA has the simpler version lane keep assist which vibrates. I have mine switched on.
The C , E, S etc. have the ACTIVE LANE KEEPING ASSISTANCE which provides corrective assistance if you fail to do so yourself. The next step on E and S is the STEERING WHEEL ASSISTANCE which will steer the car for you on motorways. Not sure I will be confident enough with that.