Each new card adds a little earning power and a little complexity. After a certain point, the complexity grows faster than the rewards, and the wallet starts working against you. Knowing where that point sits is what keeps a strategy from sliding into busywork.
Where the curve flattens
The first couple of cards capture most of the available value, as "Building a two-card system"describes. Each card after that returns less than the one before. The curve flattens quickly, which means the marginal card is rarely as valuable as it first appears.
The hidden costs of more
Additional cards bring annual fees, more to track, greater mental overhead, and points scattered across programs. The annual-fee piece of this is examined in "Annual fees are not what you think they are." These costs are easy to ignore individually and significant in aggregate.
The points-fragmentation problem
Spreading your spending across many cards splits your balances into smaller pools. That makes it harder to accumulate enough in any one program to reach a meaningful redemption. Concentration can be more valuable than breadth, precisely because redemptions reward a focused balance.
When more is justified
Genuinely distinct needs can warrant additional cards, but the bar rises with each one. The more cards you already hold, the stronger the case a new one must make. More is sometimes right; it is just rarely as right as enthusiasm suggests.
The discipline of subtraction
Sometimes the best move is not adding a card but closing or downgrading one, a decision covered in "When to downgrade, when to cancel, and when to keep paying the fee." Pruning a wallet can improve it as surely as adding to it.
Beyond a few well-chosen cards, you're usually buying complexity, not value. Know where your curve flattens.
