This is my own reflection & opinion on this topic, and it does not mean that others think like me ! What the heck, who cares !
In my own nature self, I don't usually smile, because I perceive that I won't look good when I smile. Besides, I think I look "cool" and "serious" when I don't smile, and this makes people more hestitant to disturb me, especially when I am seriously on a job.
One ex-colleague ever gave me the nickname of "Mr Serious" as I don't smile much in the workplace. One trainer ever told me I had a pan-face, and he said I could create more laughters when I tell jokes with this pan-face. OK, at least, one good point for not smiling & looking serious.
Whether or not, your smile would looks good, depends a lot on your face structure, i.e., how your eyes, nose, mouth, ears are layout on your face. Just observe people who smile. Some smiles look pleasant, some won't. Some people has a natural smiling face. Some don't. Some people, even, if they don't smile, they could still create laughters, like the guy above.
But some people has smiles that are very artificial,.....& fake. We call these people "smiling tigers" or "knife hidden in the smile". These people are usually very dangerous people to work with & you never know what is up in their "sleeves", or mind.
Many organizations set KPIs, to measure performance. But I think organizations never set SMILE as an indicator to measure how many of their employees actually smile each day at work. I strongly believe happy employees tend to smile more often, are more productive, and have less problems at work.
If you work for powerful people, this smiley indicator could also tells you if your boss is happy, & everything is ok,...If doesn't smile, or worst still, he sulks with a "black-face", then u know something is not ok, & perhaps a "great storm" is coming, & somebody's head would roll,.......
When you join a new organization or a new group, your smile could make you new friends.
You never know when you would need one another, to solve problems and puzzles at work. These 3 women work in the same organization but I have never seen them taken any photograph together. So I drew them together to commemorate their friendship and teamwork in solving a work-related puzzle.
Not everyone could smile though. Some characters just cannot smile in their usual self, like Spiderman. Can you imagine how he would look like if he smile ??? He would look funny, right ? But I still don't know why I like to draw this superhero who always hide behind a mask.
In the 70s & 80s, Master Q was my favourite comics as he always give me humour and put some smiles on my face. This character was created on the same year that I was borned. I believe the artist is a humourous person who has already passed on for many years now as there has been no more new editions released for a very long time that I could remember.
Here is one example of a cartoon that I redrawn in 1975. If I could sell it one day & make some money out of it, I'd definitely smile. But I also know, artists never make good money when they are alive, unless you'r damn good at your artwork.
I observed that models on fashion cat-walks never smile. Especially female models.
I'm not sure if they are unhappy in the job, or they are not allowed to smile at all.
Perhaps, they'r stressed as they know that such career has a very short life-span, & perhaps they'r always thinking about their next career move. Also, I have never seen any old-age models who are successful. 
People has strengths & weaknesses. What strengths do u have ?
Well, your smile can be your strength too ! It could bring you new friends, improve your working relationships and perhaps accelerate your career path.
But it could also be a dangerous weapon. Beware & be careful of people who use it excessively and irrationally ! There must be a reason for it !
People usually smile when they'r taking a family photo. They often want to leave a good impression that they are happy. Do you have a happy family portrait to keep ?
If you have a happy family, a good job, excellent boss, have all the things you wanted, well,....SMILE & enjoy life ! 