There are a few reasons why we might compare ourselves to other species. One reason is that it can help us to understand the behaviour of those creatures better. If we can figure out how they act and what makes them happy, then our own behaviour can be improved accordingly.
Another reason for making comparisons is to try and find similarities between ourselves and other creatures. Sometimes, these similarities may be accidental – for example, two species might share some physical features which make them look similar. But at other times, we may be looking for more substantial similarities. These could be based on things like the way that both species interact with their environment or the way that they think about life.