A constraint in the system that limits the flow of work.
Identifying bottlenecks makes it easier to reduce their impact and provides a mechanism for controlling work flowing through the process.
Burnout.
Frequent bugs on production.
Complaints about productivity.
Low throughput.
Leads to vague sprint planning.
Too much work stuffed into one sprint.
Unidentified bottlenecks.
Lean philosophy regards everything not adding value to the customer as waste (Muda), Such waste may include:
Partially done work.
Extra processes.
Extra features.
Task switching.
Waiting.
Motion.
Defects.
Management activities.