I've been doing this since the raid started and my stamina is sitting pretty at 5,000 everyday. Yes it's sweeping. Just to get it out of the way, every 200 stamina used ( 8 sweeps of -25 stamina ) it will discover a raid. We get 10 boosters a day, and boosters are best used on raids we've discovered. That being said we want to spawn at least 5 raids from story, 5 from shop, and the rest of our battles should be slayer raids without the boosters.
2☆ units, no armor no gear, sweep 4 times =100 crystals Swap out units and go 4 more rounds. If you used another set of 2☆ units that's 200 crystals and 1 raid boss. During Hot time we're done in 2 sweeps. . . . With 3☆ units it's 12 sweeps to max level.....
In the image I did 8 sweeps. Never do more than 8 sweeps at a time. 8 will spawn the raid boss. After the boss battle, I sweep 4 times more times for the 150 crystals. Then... For efficiency the next sweep will need to be 4 times, bringing us back to 8 sweeps in total for another raid boss. Then after....another 4 sweeps to complete another set of 3☆ for yet another 150 crystals. So far in this example that's 500 crystals and 3 raids. It's really okay to blow away 1000 stamina a day doing this FOR NOW cause we're in a stamina event. 100 stamina extra a day i think. If a narritive dungeon is coming or another raid, we'll want to adjust our sweeping routine in advance so our stamina has a chance to grow. Of course hot time is the best for this, the units cap out in half the sweeps. . . Is this good to do ? When asked I'd say yes, because this raid, I'm not just burning the excess units for onyx, I'm making significantly more crystals than you, while my stamina regenerates back to where it was by the time I do it again. You'd rather save stamina and lottery spawn the raid boss the old fashioned way ? Okay that's good too, this is just a way of making more crystals and getting the most out of the excess units we're getting daily from the free 10x summon banner. By the time you've discovered the 5th raid boss, then you'd have used 1000 stamina IF you've done this efficiently. Unless you don't mind a decline in your stamina it's best to stop here. If you don't do this efficiently, then you'll be wasting stamina. Sometimes we sweep 8, or 4, or 2 or 6 times. - If you lose count sweep twice until raid boss is discovered or units cap. - If you suck at keeping track. Then keep sweeping twice until raid boss is discovered or units cap. 2☆ = Done in 4 sweeps ( Hot time 2 sweeps) 3☆ = Done in 12 sweeps ( Hot time 6 sweeps) 4☆ = Done in 24 sweeps ? I Forget, but this one no good. Less is more. If you have the 2☆ units during hot time you can have 2,000 crystals after discovering 5 bosses.