On a date, how you carry yourself matters. The same is true with what you are wearing. This does not mean that you will have to slip on the most expensive little black dress in town or fit in that very elegant shoes that a Hollywood celebrity recently wore in an awards night.
Dressing right means dressing to the occasion. If you were invited to watch a hockey game, a tight fitting dress, even if you look really lovely in it, would not match the venue. You might just find yourself shivering or uncomfortable as you cheer for your team. If the date venue is a fine dining restaurant and you are in your jeans and fave T shirt, you might sink into your chair once you see people in their elegant formal attire. In the first place, you might be denied entry for improper attire.
It is always best to ask your date where you will be going so that you can match your dress. You do not want to be either under-dressed or over-dressed, do you?