>>56933752Incenses give +1 spawn to the up to 8 spawns you can get from Drowsy Power alone, but when you're starting out you're likely to only get round 4-7 spawns.
An incense will guarantee you get at least a 1 star spawn, but to get anything higher requires that you have a higher rank and drowsy power (of which the requirements are not communicated in-game, relying on outside info instead).
Higher grade sleep styles grant more research EXP and dream shards, especially if it's for an evolved species with higher requirements.
As such, using such an incense earlier means you're receiving fewer rewards earlier, than potentially greater rewards later on.
Incenses also have uses for completing missions or earning greater rewards during certain events featuring "Event Exchanges".
Incenses of course are also useful for trying to discover sleep styles that are missing from your Sleep Dex, so using them wisely is key.
On top of that, this week's event features a "use 7 incenses" mission to earn 20 Eevee candy.
Do not waste your incenses trying to complete this mission, Eevee candy are among the most common and abundant in the game and long-time players may have near or over a thousand of them.
I mention that specifically because earlier on they give out valuable incenses like Focus Incense (2x Research EXP), Luck Incense (2x Dream Shards), Growth Incense (2x Pokémon Sleep EXP), and Friend Incense (1 guaranteed hungry Pokémon during snack time). It is not worth burning these, they're best saved for important events like those with legendaries with potentially huge payouts, or Good Sleep events with 3x Sleep EXP.
However, Recovery Incenses? They're perfect for "use 7 incenses" event missions, due to how you receive a free one every week if you maintain your bedtimes.
Also, unless you get extremely lucky with the Sylveon spawn during feeding time, don't expect to befriend the first one you see.
They need 20 points to befriend.