Pros
You don't have to take anyone on if you decide against a particular job and they will send you to someone else.
The elderly may let you leave early if you've finished and even give you a day off. It is up to them. However, they usually do this in exchange for cleaning jobs that are not part of your job description.
Cons
Although you are called a carer, the work is mainly cleaning. All the elderly I worked for mainly, or only, want cleaning in their home. Dusting and cleaning the floor. It is just lighter cleaning than a regular cleaner since you are not expected to move heavy furniture such as the fridge. However, a cleaner gets paid double an hour and you are basically cleaning for minimum wage. On the odd occasion they might want shopping or to be accompanied to the doctor. I worked for several elderly and they all wanted and expected me to clean their home so they don't need to pay a cleaner.