Hold onto them if you dare
Despite what the name says, cells are actually the lifeblood of Dead Cells. They’re the only way to permanently upgrade your character — little by little, and level by level. Escaping each stage comes with a few different waves of relief: You get to fill your health all the way back to full, you get to upgrade your weapons and (maybe) pick a new mutation, and you get to bank those cells you collected.
But, you don’t actually have to bank them! Dead Cells makes it seem like you have to. There’s a door that won’t open until you’ve spent every cell you’ve collected. But, you can just break that damn door down. The game never tells you this, even though it seems completely obvious in hindsight. If you’re comfortable with the constant threat of losing everything, you can just haul those cells around from level to level.
There’s one major advantage to this. After every boss level, there’s a forge that appears in the safe room. The forge lets you dump cells into a meter that raises the frequency of plus-tier items. Once that’s upgraded a bit, there’s a meter for plus-plus-tier and another for S-tier. This is probably the most effective way to continually get better gear drops.
But it’s also the riskiest. Defeating a boss will net between 12 and 20 cells; the three meters combined need 12,500 cells to completely max out. That’d take more than 600 boss encounters. However, for anyone who’s comfortable enough to lug all those precious cells without safely depositing them, it’s easy to drop off more than 100 cells after a boss. It’s just another instance of risk/reward, which is the very foundation of Dead Cells.