what are the weaknesses of five point scales?

Answer 1

The major weakness of 5 point scales (Likert scales, I assume you mean) are that they are ordinal level data and NOT interval like most people want to use them. That means you CANNOT find an "average" response like, 2.5 by summing up the responses and dividing by the number of respondents. All you can do is report the frequency of responses in the various categories. This can be very valuable info in and of itself, so don't discount it.