There are several reasons to use MongoDB's improved time series collections, including their purpose-built design for handling the challenges of time series data, the ability to keep everything in house in one data platform, and logical ways to organize and access time series data. This is achieved through features such as columnar storage, efficient query rewrites, and densification and gap filling capabilities. These capabilities enable developers to build efficient algorithms, such as those used in algorithmic trading and IoT applications, where real-time data analysis and processing are critical. MongoDB's developer data platform also addresses challenges associated with time series use cases, including scalability, change streams, and functions, making it an ideal choice for organizations looking to work with time series data.