Due to liquidity constraints with some tokens, ideally one is zapping one of the tokens in a liquidity pool. For such LPs, Zapper conveniently can split your liquidity provision into whatever proportion the LP calls for (ie 50/50 in Uniswap or maybe 80/20 in Balancer).
However, Zapper also can magically Zap a token not in the pool by swapping it first for a pool token. For example, in the ETH-DAI pool in Uniswap, one could zap in with USDC. Currently, we offer this convenience with more liquid tokens like ETH, DAI, USDC, USDT, and WBTC.