The short answer is that relative to real leather, bonded leather is considerably less hardwearing, with a shelf life of in the region of 2-5 years (versus a lifetime for certain premium leather products).
When you think about it, this makes a lot of sense. After all, bonded leather is generally a composite of bottom-grade leather scraps and plastic. The PU used is renowned for its inelasticity, meaning consumer goods made from bonded leather are prone to scratches, peeling and flaking over time. Couple this with that the PU binder makes it near impossible to condition or treat the material, and you can understand the inherent limitations.
Having said this, once again a degree of nuance is required. For example, a bonded leather chair made from 70% real leather is likely to have a superior shelf life to one constituted from 10%. While certain manufacturers may adopt processes that lead to a better quality product.