You need to understand the nuances of overallocation. It is not as
simple as whether or not somebody is allocated at over 100%
In simple terms, a resource is overallocated if they have more work
assigned to them in a period than they can physically achieve in a
period. For example, If they were assigned to attend a two hour meeting
first thing on Monday morning and they were also assigned to produce a
report first thing on Monday morning, then they clearly can't do that,
yet they may well not be allocated 100% for that day.
You of course may not care about the granularity described in the
example above, because your resource can attend their meeting and
produce their report afterwards. You generally won't need to spend time
managing that fine level of time interval.
You may well care if they have more work on a particular day or week
than they can physically achieve in that period. The first thing that
you need to do is decide the granularity at which you intend to manage
your resources. You can set this under Tools/Level Resources. In the
Levelling calculations area, you can set your period of interest to be
day-by-day, week-by-week and so on.
Now having set the period you care about as described above, any
resources that are overallocated with respect to the granularity you are
interested in will by highlighted by a yellow diamond in the indicators
column and you then need to work to manage that overallocation.
Basically, you will need to level to ensure that the totality of work in
the selected period doesn't exceed the work the resource can actually
carry out.
If you expand the timescale in the Resource Usage view to a finer
granularity, you should find that where there are overallocations there
are periods where the resource has been scheduled to carry out more work
than is possible in the period (although you might have to expand it to
hours or minutes to find them when the plan becomes unmanageable).
