I like this short video here mesos learning material
with bare metal clusters, you would need to spawn stacks like HDFS, SPARK, MR etc... so if you launch tasks related to these using only bare metal cluster management, there will be a lot cold starting time.
with mesos, you can install these services on top of the bare metals and you can avoid the bring up time of those base services. This is something mesos does well. and can be utilised by kubernetes building on top of it.