I am being interviewed, and was asked to prepare a short technical presentation about any topic of my choice.
What is the purpose of such assignment and what points should I take into account when preparing/giving the presentation?
Context
The position I'm applying for is that of a software engineer.
As far as I know, this concept was popularized by the book Peopleware, in chapter 16 it has a section called "Holding an Audition". It's only a page and a half long, so if you have an interview involving this, it's probably worth your time to read it. Here's the summary: even in technical positions, most people spend a large portion of their day communicating with coworkers. The purpose is to evaluate a candidate's ability to communicate with their coworkers. If the company is following the advice in the book, the audience will be composed of people that would be your peers.
With that in mind, you should then create the presentation as if you're presenting to peers (albeit potentially ones with more or less experience/knowledge than you).
Be brief, clear and to the point in your presentation. Keep it interesting and don't overwhelm your audience and remember that you present yourself too.
Some of the purposes to this task are obvious:
These are easy to understand and incorporate in your presentation to present yourself in the best light.
Other details that interviewers may be looking for are less obvious and need more thought:
Let me explain what the less obvious facets of these questions are: It's all about what you think noteworthy about your skills and knowledge.
The presenter omits certain parts completely? Maybe they don't even know how to do those.
The presenter elaborates at length about rather mundane aspects of the trade? They might not be as senior as they present themselves.
They go on and on about all the big paradigms you included in your work? Maybe they they like to use each and every tool in their tool box to get that thumb tack into the cork board.
These aspects can influence the picture you are trying to shape.
tl;dr: This is a great idea and you should probably take it as a compliment that you made it to this level in the interview process.
What is the purpose of such assignment ...
There are plenty of good reasons to have a possible new hire do this:
Is there anything that they feel strongly about at all (technical or otherwise)? If not, they're likely not an interesting person to work with.
Can they string enough sentences together about their favorite topic to fill a Powerpoint presentation? If not, it's highly unlikely that they'll be able to write work-related words and will be nearly incapable of presenting concrete ideas to the team.
Can they get up in front of a group of people and speak at all? Many people are deathly afraid of public speaking. Can this person make the mental transition from "I'm doing public speaking" to "I'm talking to my team and this is an important part of my job"? If not, they'll never be able to take even the smallest leadership role: if you can't talk to a group, you can't lead an effort.
Can they respond to questions and critical feedback? There will almost certainly be questions during the presentation (unless the topic is toxically banal, putting everyone to sleep). How do they respond in this situation? Are they defensive? Do they panic? Are they constructive?
In short, this is a great way to start a conversation with a possible new hire in a venue that's not an across-the-desk interview. The candidate gets to choose the topic and style (within some bounds, I'm sure). The audience then gets to participate as a group in the discussion. This is an excellent distillation of the standard team effort.
... what points should I take into account when preparing/giving the presentation?
There are several questions and points you should probably clarify before the presentation:
Who are you talking to? Senior management? The team that you'll be working with? This can drive the formality vs. chatty style of your presentation.
What's the venue? Big room vs. small room, do you need a pointer or can you just point to a screen to make a point?
How many people? If it's a huge room (and I doubt it is), you might need to wear a microphone to be heard in the back.
What's the technology for the presentation? Powerpoint? Mac vs. PC? Are you handing them a disk of slides? Will you be clicking next page or will someone else be advancing the slides?
Will you have some setup time before the presentation? You're going to be nervous so take as much time as they offer to get all the technical ducks in a row.
Make it clear that you cannot present any sensitive information from current or prior employers. That will come as no surprise but it's a level of maturity that not all candidates will show.
It's purpose is for you to demonstrate technical knowledge (or any knowledge if it's that broad), level of comfort with it, enthusiasm (which is hard to hit on in standard interview Q&A) and ability to accept and deal with challenges to your propositions. If it's a senior position they'll also be looking at your presentation skills and confidence, otherwise they'll overlook the extra nervousness.
They'll be expecting...
They wont be expecting...
