The SMAS is considerably apparent in the buccal, temporal, zygomatic, and platysma regions. Thus, the corresponding muscles correlate or serve as an anatomical border to the SMAS. 

The SMAS additionally invests smaller and more intricate muscles. This muscle group includes the orbicularis oculi, orbicularis oris, the occipitofrontalis, and the levator labii superioris muscle. 

The forehead, nasolabial folds, and nasal regions are usually not included under the SMAS, although literature reporting several anatomical variants involving these muscles are available.

There are several physiologic variants of the SMAS, but the bulk of differences seem to exist due to lack of uniform large-scale cadaveric studies employing histological and macroscopic dissection. The study by Khawaja et al. analysed the SMAS during 800 facelift procedures. They used the term SMAFS which stands for the superficial musculoaponeurotic fatty system instead of SMAS. From this research, they concluded that Six definite SMAFS variants exist. These six variants are - membranous, fatty, mixed (membrane-fatty, fleshy-fatty, among others), island (broken), fleshy, and fibrous. The variants described in this study are mainly due to the diversity in the deeper fatty layers of the SMAS. Some variants may be due to congenital anomaly or atrophy and breakage from repeated botox injections or even steroid use. They determined that the variants of SMAFS had an impact on the procedure and outcome of facelift surgery. The operative technique of plicating, lifting, debulking, and attaching the SMAFS to the bony periosteum has to be according to the type of SMAFS present, which is necessary for suitable cosmetic and surgical success.[4]

The SMAS plays a vital role in the rhytidectomy, frequently known as the facelift procedure. Surgical manoeuvring and tightening of the SMAS allow for complete facial rejuvenation. The SMAS is more valuable to the enhancement of the lower third of the face than the midface. The clinical utility of the SMAS is primarily recognised in aesthetic surgery and employed in procedures to reverse age-related drooping of facial fat. These surgeries involve the superior elevation of the SMAS to elevate superficial dermal and muscular structures. Case reports suggest that 50% of all rhytidectomies consists of at least some type of SMAS manipulation and dissection. The studies hence portray the clinical and surgical significance of the SMAS in cosmetic and dermatologic surgical procedures[7][8][9][8].

As described previously, there have been numerous attempts to delineate and provide a more clear anatomical definition of the SMAS. However, inconsistencies exist not just regarding its anatomical location, but of its general morphology and basic terminology as well. There are even some researchers who doubt its existence. One of the main disagreements involves zygomaticus muscle investiture by the SMAS. Machi et al. reported through histological studies that the SMAS does indeed invest the zygomaticus muscle, while Gassner et al. argue that it does not. Another inconsistency often discussed is its continuity with the parotid fascia. Previous studies are somewhat inconclusive on this point.

In contrast, the majority of recent studies concur that the SMAS is an entirely separate layer that lies superficial to the fascia of the parotid gland or parotideomasseteric fascia. The anterior relationship to the nasolabial fold is also controversial. Still, most agree there is continuity with the nasolabial fold and even extension into at least some part of the orbicularis oris. Despite these discrepancies, the SMAS certainly plays a vital role in providing facial elasticity and support, while also facilitating coordination of muscular activity of the cheek.[10]