After taking a TEFL course I flew to Taiwan to find a job teaching ESL. I started off teaching English in Taiwan as a substitute teacher. Until I did I subbed in a number of different schools and did monthly visa runs. While I was subbing I was also looking and applying for jobs that would give me a visa to stay in Taiwan.
Subbing is a good way to get some experience teaching English abroad. If you are not ready to commit to signing a contract for a year then subbing or teaching part time is an option. Or if you are traveling abroad and considering it then do it. You can get your feet wet without all the sudden stress of taking on a new job in a foreign country.
1. There is no commitment
Well, there is no long term commitment. You don't have to sign a contract. Most sub jobs are just for a day or two or maybe a week or longer if someone is on break.
2. You get paid that day
Most of the time you get paid the same day unless you are subbing multiple days. But even then if you really need the cash you can probably negotiate that with the school. I found private schools in China, Korea and Taiwan that were always willing to do this. This is good if you just arrived in a foreign country. You'll get some money then and there and you won't have to wait a month or more to get your first check.
3. The workload is lighter
It can depend on the school, but since you are just a sub you are not usually expected to prepare an extensive lesson. It's usually pretty easy going. Often you will just do some review and play some games and activities with the students.
4. There is less pressure
Since you are just a sub and temporary the school is unlikely to bother you much. You are just filling in for the regular teacher. In most cases the school is happy to have you there as a replacement. If they don't have a native English teacher then parents aren't going to be happy.
5. You get to meet other teachers
In most schools there will be other foreign teachers like you working there. You can get a lot of ideas from them on how to handle problems you had and you can make friends with them. They will have more experience than you and they can usually help you out one way or another. They may know of another school that is hiring full time, be able to help you find a home or whatever.
6. You can get ideas from your students
Not only can you get ideas from the other teachers you can get ideas from the students in your class. Your students have had many teachers before you and they have learned many different games, activities, exercises and so on. Remember that you are in control of the class, but don't be afraid of asking them for suggestions when you need. And just listen to them you'll be able to pick up on stuff from them.
7. You get to check out different schools
When I first started teaching as a sub I worked in kindergartens, buxibans, and public schools. I got to find out about what I liked and didn't like. For example, while I liked the morning hours of the kindergarten I was subbing at I didn't like the large classes of almost 40 little kids. I found out that no two schools are the same. It's also another way that you can find out if you prefer teaching children or adults.
8. You get teaching experience
9. You get more time
If you are not ready to sign a contract then doing some subbing here and there will give you some money until you are. If you need a school to get you a visa then you will pretty much have to sign a contract. Having the extra time will be good for finding a good ESL job.
In the end subbing is a great way to get started as an ESL teacher. You can make some cash, meet other teachers, check out different schools and get some experience without making any commitments.
Sometimes it's good to just jump in and commit, but if you are sitting on the fence or you want to ease into it try subbing. And if you are just starting out I'd recommend taking an online course in addition to the subbing.
It will be better to combine online training with actual on the job teaching not the pseudo 6 hours kind you get in a lot of "in-class" TEFL courses, but with the students you are teaching.