The Player's Handbook (p. 101) states (about flexible casting):
Creating spell slots. You can transform unexpended sorcery points into one spell slot as a bonus action on your turn.
I'm unsure how to interpret this in practice. Does this mean that you can gain more spell slots than you would normally have available after a long rest, or would you only be able to regain expended spell slots up to your normal maximum? And if the former, would the excess spell slots be lost on a long rest or not?
Best Answer
How to interpret the Sorcerer's Flexible Casting ability that utilizes Sorcerer Points to create Spell Slots:
Which doesn't go to say that every spell ever that takes a bonus action or action on your turn can't be used out of combat, but we can assume they stress this point due to its combat applications. Creating or burning spell slots doesn't have too much out of combat usefulness. You would interpret this as a combat ability, and an out of combat utility that can be useful in certain situations.
Each Spell Slot that you are able to craft through the use of Sorcery Points takes an amount of SP only acquired once you are of sufficient level to even have that level of spell slots available to you. So while you could never have a spell slot that's beyond your ability to use at the time, its primary use is replenishing spell slots that you've cast or otherwise used up in battle (as when you burn one to gain more SP so you can put them into a Meta Magic ability). They do not roll over , as it were, as taking a long rest basically returns everything to its normal state. Extra spell slots disappear, Temporary HP disappears, and any temporary buffs or bonuses that were applied through magical means disappears; unless it has an effective duration exceeding your Long Rest period. Flexible Casting spell slots are no different.
So yes, the rules don't say anything about not being able to exceed your normal maximum allotted spell slots. Taken as written, if you wanted to burn all your SP at the beginning of a combat to gain all those extra spell slots, you could do so, but yes; they are lost on a long rest. No slot hording for you!
I hope this helped in your interpretation of the ability and the rules. I have a Sorcerer in my adventuring party and I'm kind of jealous of his raw magical power. He's a beast with those Twin Spell and Quick Spell Meta-Magic feats, and we won't even touch on Magical Missile...