With a month to month lease, you are able to have a bit more flexibility if you are not a fan of who ends up moving into your rental property. While this shouldn't be the main reason for you doing a lease in this way, it is certainly something to think about. The main draw that most people find with a month to month lease is mostly dependent upon the location of the rental property. If you are located in a large vacation area, then having a lease that is only a month at a time will allow you to charge a little bit of a higher rent for those peak months as opposed to one flat rate for the entire year. You can find tourists and others who are looking to take an extended vacation quite easily and they are normally willing to pay a little extra than those who are looking to move in for a full year.
Another great thing about having a month to month type lease is that your tenant can let you know ahead of time how long they expect to stay. If their work is bringing them to this area for six months, then you can be sure to keep someone in your space for that time. It gives you a set time frame for when you need to bring someone else in and start showing it to other people. It's also fairly common that someone will look for an apartment for longer stays like this as not many people like to stay in a hotel for that long.
If you are debating between having year or longer leases or going month to month, then ask around and see what other people have experienced. Try it for yourself too. You never know what you may find that you like until you try it.