Due to their construction with a single reed, Clarinets (and also Saxophones) have the special ability to create incredibly low dynamics and can crescendo from or decrescendo to almost complete silence. This doesn’t only apply to the Clarinet in Bb or A but also Bass and Contrabass Clarinet, as well as Clarinet in Eb or D.
This makes it possible in orchestration to only “hint” a note in soft passages which can create fascinating effects. But also dynamics with true silence on one end can create fantastic effects. In the orchestra, the only instruments that can create comparable dynamics are the strings, with any other woodwind instruments as well as brass you will always get a more or less defined start and ending points of notes as it is simply not possible to keep a tone alive below a certain degree of air flow.