There are definitely some downsides to overtime:
-The team may start to burnout
-The increase in velocity may become an expectation
-It can lead to a decrease in performance/productivity/morale
-Poor work-life balance
-It can be an indication that the organization is unwilling to pay for additional resources
However, there are some upsides:
-Some people appreciate the extra income
-It may not seem like a heavy lift when others are doing it as well
-It may prevent a death march ending
-People typical save money because they’re unable to spend it like they normally would
-It can allow for flexible hours which may be handy for parents with young children
-Allows people to improve their skills
So is Overtime and Agile anti-pattern?
Accordingly to XP (Extreme Programming) the aim is for a sustainable pace.
Furthermore, if overtime is required in one iteration it should not occur in the next.
So as long as the overtime is controlled and doesn’t get out of hand (e.g. 80 hours/week), Agile teams should not feel they are operating in an anti-Agile environment.
It is not uncommon for teams working in a 2 week iteration to evaluate their progress after 1 week. If they are behind, they may decide to work some overtime before starting the 2nd week.
This allows them to get back on track and the sprint goal is no longer jeopardized.