/u/shashwathj, everyone here is answering the wrong thing.

30 respondents is a rule of thumb for when you can use the normal distribution as an approximation for the binomial distribution.

If you have a survey that is asking a yes or no question, that is two options so the distribution for that is the binomial distribution. The binomial distribution is a bit of a pain to work with however but fortunately it starts to look like the normal distribution with more and more respondents. To give non-statisticians a simple threshold for this, we say 30 respondents.

The normal distribution has a simple (by mathematician standards) equation for confidence intervals and so you can quantify the uncertainty in your survey.

There are other methods for confidence intervals with smaller sample sizes but we can't teach everyone everything.