De sysfs.txt :
sysfs is a ram-based filesystem [...]. It provides a means to export kernel data structures, their attributes, and the linkages between them to userspace.
Em essência / sys, você pode obter informações sobre o sistema e seus componentes (principalmente hardware conectado e instalado) de maneira estruturada.
Veja também o Artigo da Wikipedia sobre o sysfs . A seguinte declaração deixa bem claro:
sysfs is a virtual file system provided by Linux. sysfs provides a set of virtual files by exporting information about various kernel subsystems, hardware devices and associated device drivers from the kernel's device model to user space. In addition to providing information about various devices and kernel subsystems, exported virtual files are also used for their configuring. sysfs is similar to the sysctl mechanism found in BSD systems, but implemented as a file system instead of a separate mechanism.
Veja também esta excelente resposta para Qual é a diferença entre procfs e sysfs? no Unix & StackExchange do Linux.