Significance of max_utilization in dbrm

Hello expert,

                   In one of the oracle documentation I found below.

Within a particular level, CPU allocations are not fixed. If there is not sufficient load in a particular consumer group or subplan, residual CPU can be allocated to remaining consumer groups or subplans.

Ref:-http://docs.oracle.com/database/121/ADMIN/dbrm.htm

Suppose I have one level and I have 3 consumer groups like below where max utilization limit is not set

cg name cpu allocation%

oltp                80

others            10

sys_group      10

Does that mean if my sys_group,other_groups are not actively used then oltp group can eat up 100% of cpu?In that case any backup job will hung.Please clarify this