Destroying or rendering nonoperational 10% of an enemy force is routinely referred to as "decimating" (reducing by a tenth) it. It should not be casually dismissed or minimized.
Besides the tangible effect, it also has a tremendous impact upon morale.
Regards,
"Decimating" is an old Roman term not used by modern military forces, which tend to go with "neutralized" for 10% casualties, and "destroyed" for 30%. That is based largely on the axiom that each soldier killed or wounded (especially the latter) takes 2 others to care for/transport him.
But it's important to realize that those are short-term statuses from which units can reorganize and recover. They don't get the troops back, and so are not at full-strength. But they can easily become operationally capable again even if they've lost 30% of their starting strength.