Your vendor likely did this to try to gurantee resources for these in times of contention. Resource shares have 0 effect if you aren't resource constrained (which, as you say, you aren't), so for now these are not kicking in.
What you set them to is a matter of policy. You can use the Low/Medium/Normal/High options given (which just correspond to default #s), or set your own values.
Prioritize appropriately but in general I would recommend to avoid setting custom shares. Reset everything to the default "normal" and see how the environment behaves. Based on the the behaviour select the appropriate actions which might be a reservation or increases shares level.
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First of all there is no silly questions and nothing to feel stupid. Shares come into existence when there will be resource contention otherwise your VMs will keep running as per the allocation.When the resource contention happens then VMkernel look for the shares of the VM and decide the allocation accordingly. Shares could be High Normal and Low in the 4:2:1 ratio.Apart from this custom is something which admin defines to guarantee the allocation.When there is confusion as what is better then you should always choose "Normal" as the share.This will ensure that the VMs do not crib as well as do not get overallocated when there is contention.