While Dungeons & Dragons is primarily a fantasy escapism game of monsters and mayhem, there's still plenty of number-crunching and paperwork to do so a player can survive a campaign. In between fun character roleplay and exploration, a player must juggle all their resources to make sure their character is ready for action. For spellcasters, that means managing spell slots.
Source:https://www.cbr.com/dnd-spellcaster-spell-slot-management/