Purposive samples target a very specific population, which can help gain detailed insight on their characteristics, but a disadvantage is the difficulty in reaching a large sample size. Defining the target for purposive samples can be difficult, as all targets may not be known.
Purposive samples are surveys that are looking to evaluate the characteristics of a large target population. This is because it often isn't representative of the larger population. Often times, purposive samples are referred to as a snowball sample. The best way to gain insight into other members of the target sample is by asking the current person the researcher may be interviewing, creating a snowball effect with the number of targets.