It's VERY important. Volume to the ear is perceived to be doubled at roughly 9-10 db increases in output. Now, how that works (or is overcome by) just power.
Take a 100 watt per channel amp ( all other things remaining equal/constant) with the intention of doubling the perceived volume.
100 to 200, 3 db increase.
200 to 400, another 3 db increase
400 to 800, another 3 db increase or very close to a perceived doubling of the volume.
Why is that important?
People will often try to 'wattage" out or use power to overcome the noise with that additional power. First, if you could find an 800 watt per channel amp, it would likely cost several thousand dollars not to mention the array of speakers (another several thousand dollars) to utilize all that power.
That said,
While a single layer of half-mil thick butyl rubber applied randomly around a vehicle may only lower interior noise levels by
2-3 decibels (dB). A professional 3M DBA or Resonix installation is capable of an
8-12dB reduction in average road noise levels inside the vehicle cabin.
So multi-thousands to overcome noise through output that drowns out (does not eliminate) noise or $250 to $750 to eliminate it in the first place and have that 100 watt per channel play like it is a 800 watt per channel system in a noisy car.
Kind of puts it into perspective, don't it?