In the 2.4GHz spectrum, channels are spaced 5MHz apart but have a bandwidth of 20MHz, resulting in overlapping channels. To minimize interference, especially in a dense environment where access point coverage overlaps, a narrower channel width of 20MHz should be used. Using wider channel widths like 40MHz, 80MHz, or 160MHz in the 2.4GHz band will increase the overlap and interference. The 20MHz channel width provides a good balance between performance and minimal interference.
Reference: CompTIA Network+ Certification Exam Objectives - Wireless Networks section.