Why it is necessary to buy a deep cycle battery pack, and what is it useful for?

Insight on deep cycle battery:

Deep cycle battery packs might look a good deal like automobile batteries to people that aren't accustomed with them, yet they're one-of-a-kind in all actuality. It's a lead battery intended to give sustained control over an extensive stretch and run till it is 80% released or much more, so, all in all, it must be re-energized. 

https://www.smartyblogs.com.au/why-do-you-need-a-deep-cycle-battery-pack-and-what-are-its-benefits/