Having worked as ground services and now as cabin crew there is one thing that always becomes a hassle but can easily be avoided.
Guests that are disabled or have special requirements are always able to be pre-boarded before the general boarding of the aircraft begins. The only thing is that you must tell them that you require a wheelchair or whatever special assistance it is that you require.
Many people do the right thing and call up to do the booking so that a wheelchair request etc can be made (only so many can be on a flight). That way an aisle wheelchair to take the passenger on board is ready and waiting.
Once the guest(s) are checked in they must ensure they are at the gate with plenty of time. The whole thing about pre-boarding is that it happens before general boarding at the appropriate set time. If the wheelchair guest (or whatever special assistance is required) is not even through security and downstairs having coffee this becomes extremely frustrating. Then general boarding takes place and the wheelchair guests needs to be boarded last and use the slide board etc in front of a full aircraft which is not desired.
So my key message would be ensure you are at the gate early so that you can be preboarded. There is nothing worse than a special assistance passenger not there and having to go on last as they didn't go through security and the rest of it.