This percussive sound is preferable because it usually stands in better contrast to the sound being made by the instrument, i.e., a more percussive click is easier to hear. Larger metronomes often offer more features, too. The Dr. Beat type, for example, has individual volume controls for each subdivision of the beat. Small metronomes also have advantages. There is room for it in just about any clarinet case.
Batteries last a long time in the small metronomes.
Larger metronomes use larger batteries that need to be replaced regularly. The credit-card type are also nearly indestructible. Mine has been dropped onto concrete floors dozens of times and is none the worse for wear. You wouldn't want to drop a Dr. Beat from a music stand onto a concrete floor. I prefer using a smaller card-type metronome.