Is it necessary to have many slides when presenting in conference?
Slides serve the following purposes:


If the title of your paper is too long, you don't have to write the title on the board, losing time.
They keep the audience up-to-date. Gives an idea on what you are doing now, what you are going to do some time after.
Contains hard-to-draw figures. Therefore, you are able to talk to-the-point without losing time on drawing figures.
Contains experimental results. These, if extensive, literally cannot be drawn accurately onto board in about 10 minutes. Maybe they can be, but then there is no time to talk.
May serve you as reminder cards, therefore you don't forget what to talk about 2 minutes later.
In the Q&amp;A session, if someone asks you about a table, a figure or a graph, you don't have to draw them again. Rather, you can just go back and answer the question.
If you are a junior researcher, you are able to write your name and affiliation on the slides, and avoid the awkwardness of writing your name on the board as if you're an instructor and if audience consists of students.
You can always support slides by using the board, and explain your points better.


These being stated, I think slides are crucial for a presentation where the time limit is considerably low (10-20 minutes including Q&amp;A).