The answer to this question is a little complicated, as there are several factors to consider. For starters, Warlock spells are typically classified as “dark” or “light.
” Dark spells deal with the occult and evil, while light spells deal with the natural and holy. This means that dark spell slots would be better used for spells like Hex or Curse, while light spell slots would be better used for spells like Heal or Sanctuary.
However, there is another consideration to make. Warlock spell slots are not static – they can be upgraded using Spell Slots Emporiums (or other similar sources). This means that, depending on the specific spell you are using, you may end up using different spell slots for different occasions.
For example, you might use a light spell slot to heal yourself in battle, but use a dark spell slot to curse your enemies. This can be a bit of a flexibility issue, and it is something that you will need to take into account when deciding whether or not to use spell slots for Warlock spells.