When done properly, live sound is much more dynamic because you're hearing all the peaks that are taken away in the record and radio process. That is the one aspect of live sound that has always kept it artistcally creative for me - using dynamics in a way to create a pleasing flow from one section of a song to another, like bringing down certain parts of the rhythm section in the first verse so nothing crowds that precious lead vocal when it is first heard. Then bring the rhythm section back up for the chorus. As well, your standard solos or tags are always featured with a boost in volume. Your ears get fatigued of hearing the same balances all night.
Most engineers get a balance and leave it all night.
Little strategic dynamic changes in parts of the mix can be interesting during a live concert for a band like Saga, as well as great big volume changes for David Lee Roth. This is the area where you can get creative with dynamics during a show. Don't let your board stagnate.