There are a few things to consider when determining if you need to buy a potty chair for your toddler.
A potty chair is portable and can be moved from room to room or house to house, depending on where your child is. It allows your child to be more independent because he/she can go by themself since they can easily sit on it. If the potty chair is closeby, it is more likely that your child will make it to the potty chair on time rather than if he/she had to rush to the bathroom. If the chair is sitting there, your child will see it and remember to use it (most times). Some children may simply find sitting on a toilet too scary and they may be afraid of the flushing sound so the potty chair makes them feel more secure.
A drawback of using the potty chair is that you constantly have to clean it and this can be messy. If your child is large for his/her age or you are training an older toddler, he/she may have find the chair to be too small to sit in. Also, it is hard for boys to learn to urinate standing up with a potty chair because the seat is too low and it is too difficult to aim into the potty. So if you are going to begin training your son with a potty chair, toilet training will be a two-step process for you.
A happy medium between the two is a toilet seat adapter. This is a smaller version of a toilet seat that sits on top of the regular toilet seat. It is made from soft, cushiony material and can be easily removed if your child is sharing the bathroom with other family members.
Whether you use a potty chair or not is your personal preference and it is best to choose a method that makes your child the most comfortable. If your child is frustrated and stressed, then he/she will not be interested in potty training.