Adjustable suspension can mean many things, such as adjustable dampers, ride height and caster/camber.
With adjustable dampers, you can alter the bump and rebound characteristics. Ride height can be adjustable as well, using what's popularly known as coilover conversions. These are ones where a combined spring and damper unit are used but the lower mounting platform for the spring is threaded, so it can move up and down. This allows the ride height of the car to be altered at each corner. However, this system was originally designed to ensure that the static weight on each corner of race cars could be optimised.
Generally speaking, the lower the ride height, the less the car body will roll as it corners, all other factors being equal. This is because it moves the car's centre of gravity (the theoretical point where the car's total weight can be considered to act) closer to the ground and therefore, the cornering forces cause a smaller rotational force on the body.
Adjustable geometry means just that - by moving the mounting points on the chassis, the suspension geometry can be altered. Toe angles are changed usually by threaded adjusters on the end of the steering rack for the front wheels and by a similar method on rear wheels, via links acting on the front or rear of the hub. Caster can usually be adjusted by moving the top of the suspension strut forwards or backwards, while camber can be changed by moving the top of the strut towards or away from the centreline of the car. Fully adjustable top mounts will usually allow both of these.