Maintenance on an Aluminium frame
Really deep dents or cracks are a cause for concern, but not little dimples and such.

Also, the "work hardening" of aluminum is considerably less than industry types would make out....I've worked on numbers of aluminum frames that are at least 20 years old with no sign whatever of any structural problems.
Kind of depends what you're doing.  The average roadster isn't subject to much in the way of severe shocks; not so with a mountain bike being used to bounce off boulders and do 10-foot vertical drops.