Way is knowing the pelvic structure important?

It’s a good idea to note the configuration of the pelvis when creating any character, human or anthro. I'm a firm believer in sketching out the basic bone structure in any character sketch, it helps to create your anchor points and maintain your proportions. There are a number of landmarks of the hip that will dictate the overall look of your characters waist, hips and legs that are worth taking some time to study.

Landmarks from the front:
1. The iliac crest, the most obvious part of the pelvis you can feel under the skin. In an athletic character the crest forms the ridge to the bulging mass of the obliques, the muscles of your waist.
2. The inguinal ligament is formed by the obliques and demarcates the line where the torso ends and legs begin. It creates the distinctive 'V' or 'U' shape seen in the photo below.
3. Pubic tubercle this forward projection of the pubic bone can be felt under the public line and is the attachment of the inguinal ligament. The abdominal muscles also attach to the pubic bone. Below this landmark is the point at which the genitals sit, in the male for example via the suspensory ligament. (Also worth noting is that if your characters are in 'heroic' proportion, that's 8-heads high, this landmark marks the mid point of your character height).
4. The greater trochanter of the femur is the major attachment point of the gluteals. It is clearly visible in a frontal view as a bulge at the top of the leg and more predominant in the female. It adds a distinctive curve to the top of the leg when drawing characters from the front or back.

The distinctive 'V' or 'U' shape of the obliques.

Standing upright - Part II

It isn’t possible to directly compare a set of quadruped ‘buttocks’ to that of a human because for quadrupeds, like the horse in this example, their behinds are not really gluteals, they are hamstrings. I'll bang on about these muscles groups just once more:

Hamstrings: in quadrupeds serve as powerful hip extensors, driving the animal forwards against the ground reaction and pulling the leg up and backwards to take the next stride, whereas in humans their action is similar but less powerful due to them being almost vertical when stood upright. Importantly, in bipeds they counteract the truck from falling forward.

Gluteals: in a quadruped, are powerful locomotors also extending the hip, in humans these would relate to gluteus minimus and medius and are now adapted to stabilise the hip laterally, most notably when we stand with one leg off the ground, rather than being used for locomotion. In bipeds the gluteus maximus takes more of the role of hip extensor via the ilio-tibial band. Gluteus maximus also counteracts the truck from falling forward.

Take a look at the action of the race horses legs, you can see all that ground force coming from the contraction of the hamstrings at the back and gluteals at the top of the hind limb pulling them backwards and driving the horse forwards. 

The gluteus maximus dominates in humans, its function still makes it a powerful hip extensor but it’s role in stabilising, holding the femur and pelvis in alignment, keeps us stood upright. This makes it a very important muscle for bipeds. (Also worth noting that a large gluteal makes it easier for us to sit down).

Dependent on your furry character’s needs, be them straight legged or bent kneed, their gluteals and hamstrings are going to function slightly differently, be sized accordingly and maybe even positioned differently. All that is going to be aided by the configuration of their pelvis.