>To na czym Twoim zdaniem polega róznica między
>What did you do in Rome?
>i
>What were you doing in Rome?
>gdy mowa np. o krotkim wyjezdzie wakacyjnym
This is the example or situational context, if you like. With continuous :
1) it can be incomplete
2) the happening could have limited duration
3) it can be more polite ( mg )
Simple past carries no such entailment.