10BaseT switches can be consider as the first step of the network upgrade. Network traffic is reduced. Newer systems will enjoy the top speed at the 100BaseT segment. It is ready for the future. The older system can enjoy the improved lighter traffic at the 10BaseT segment.
Collisions exist in each segment.
That can cause traffic jam. Especially, when data communication across the bridge. All hosts at the 100BaseT segment need a new network adapter. It costs more. The reliability is doubtful.