There are a number of advantages to taking a siesta - not least the mental and physical well-being it can provide. It is, however, not common practice in many countries, partly out of habit, but also because there are a number of disadvantages to sleeping in the day. Some of the more common ones include the following:
Difficulty in sleeping
When not used to sleeping in the day, it can be quite difficult to train yourself to sleep at will. You may decide, for example, to nap during your lunch hour, but then find yourself unable to drop off. This can be frustrating, and, unless willing to keep trying because of the benefits, you may give up.
Inability to control length of sleep
Again, when not used to napping, it can be difficult to control the length of the sleep that you take. You could counteract this by setting an alarm, but then you may find that being woken like this can make you irritable and unable to work until you've properly woken up.
If you work in a busy office and there is nowhere that you can go to close the door and lie down, then the chances are that you won't be able to take a siesta. A few people can sleep regardless of the noise around them, but most people need quiet. If you snore, there is also the risk that you will disturb others.
People tend to have very busy lives and pack chores into their lunch hour, so that they simply don't have the time to take a siesta. In actual fact, sleeping could give you more energy and motivation to get through the rest of the day, but changing habits can be very difficult.
Affects sleep at night
You may find that, as a result of sleeping during the day, you struggle to sleep at night. You should be able to adjust by going to bed a little later, but some people find it hard to sleep unless they are absolutely exhausted. This could mean a night of tossing and turning before having to get up for work feeling tired.
Taking a siesta may well not be allowed in your workplace, especially if you only have a short lunch hour. You may be able to persuade your boss of the benefits of napping, or start working at home where your time is more flexible, but otherwise, you will not have much choice in the matter.
On the whole, it is worth trying to take a siesta during the day, unless one of the above factors precludes you doing so.