One of the most common reasons students wish to register for a class
"S/D/F" is because they are concerned a course outside their primary
interest (i.e., major) is too difficult or may detract from other
courses they feel are more important.
Registering for a class on an S/D/F basis is not the right approach
to this concern. Here's why.
In an open curriculum, taking challenging courses outside of your
strengths or major is normal. In fact, a major advantage of
the open curriculum, and of a liberal education generally, is the
opportunity to develop and exercise mental powers that are not tied
to your major.
Long experience - indeed, longer experience than my own - suggests
that registering S/D/F is counterproductive. Students often get a
false sense of comfort and drop or put off work. After all, they think
they "only" need to get a C. However, it is easy to lose track
of things, and the difference between and C and a D or F may not be
all that much. This casual disregard commonly leads to academic trouble.
Moreover, many folks reading transcripts will read an S as a C, even
if you did outstanding work. Thus for many observers (e.g., employers,
graduate schools), an S, does not add strength to a transcript.
If you are not going to put the effort into a class, you are unlikely
to do enough work for a passing grade. In short, either you do enough
work for the class, in which case you should shoot for a real grade,
or you don't do enough work for the course, in which case you shouldn't
be there in the first place.