Well it depends on what you want your survey/ questionnaire to show. Using a coding matrix such as a scale means that you can analyse the data very easily - work out percentages of strong responses, positive responses, negative responses etc.
Whereas if you ask open questions that the respondant can answer as they wish you get more detail but you then have to code the data if you want to provide any form of summary of the overall responses.
Also as people are used to using this type of scale the questionnaire can be explained simply to people either individually or as a group and they can lergely then complete it themselves whereas if you want to ask open questions and record individual responses you need to allow time to either write down all responses or to allow the respondant to record their responses.
Verbal answers are usually too convoluted and
'wordy' to be easily compared with other responses.
A numerical scale reduces every response to a
single digit, then some schoolboy arithmetic enables
one to compile pie-charts, histograms, etc. as visual
representations of the data.
A word of advice : use an even-numbered scale, such
as !-6, 1-8, or 1-10. This prevents respondents opting
for the 'average' answer, as there is no central digit.