In a straddle/strangle you have unlimited upside on both legs (up and down/call and put). It’s a matter of determining if the long gamma+long volatility position is worth the price you pay in option premium up front and decay thereafter (theta).

that's true, and a more complete explanation.

i was taking the practical view that in most cases, the underlying options are reasonably priced and volatility is not highly unusual, so the practical upside is small at best. it's easy for the non-professional investor to lose money on these because you really need some extraodinary non-public information to exploit them.