This is an especially good solution if you typically have only a few
boxes checked (= [CategoryId] values) for each of your clients.  If most
of the boxes are usually checked, however, you'll wind up with lots of
records in this Table.

You could define your [CategoryId] values, for boxes that are usually
checked, to be true if and only if the box is NOT checked.  Then you'd
store records only for the less frequent cases and keep the size of your
Table down that way.

Or you might use a combination -- check boxes in the main record for
some properties, [CategoryId] values in linked records in a separate
Table for other properties.

In any case, I suggest that you CLEARLY    identify in comments or
elsewhere, for anyone else who later has to maintain the database, or
for yourself six months from now, EXACTLY what each checkbox or category
value means.  Otherwise, you'll have endless trouble and be sorry you
ever embarked on this project.

  -- Vincent Johns <vjohns@alumni.caltech.edu>
  Please feel free to quote anything I say here.