Questions about integrating sub with monitors, power usage and driver age

When integrating a sub with speakers, does the sub reduce the load on the speaker drivers? In other words, say I have a pair of bookshelf speakers that can reach down to 60 Hz, and I combine it with a powered sub and set the low-pass cutover to 80 Hz, does it free up the bookshelf drivers by not having to reach down the extra 20 Hz? And does that then mean that more of the amp's power is dedicated to a narrower frequency range? If so, would this result in an audible improvement in SQ?

Second question, can anyone verify if the following is true?

"Unless the speaker is hardly ever used the life of a driver is typically 7 to 10 years if it's used regularly and turned up frequently. They can still make sound after that but the voice coils become worn and the response becomes mushy."

Thanks!!!