Memory speed usually refers to memory bandwidth, which does have a limited amount of impact on day to day apps as they don't usually require a lot of bandwidth.

Memory speed usually refers to memory bandwidth, which does have a limited amount of impact on day to day apps as they don't usually require a lot of bandwidth. Memory Latency, on the other hand, can have a huge impact on performance. That's the reason chips have had steadily increasing cache sizes over the decades along with the introduction of additional caching layers. What Apple's M series improves by putting the memory on chip is both bandwidth and latency. The latency, however, is what will impact app performance more than anything else. Latency improvements are the reason memory controllers were moved from motherboard northbridges into the CPU IC. Shortening that distance means a lot to shortening latency.