Yes - offset is important. Presumably you are asking this about the Euro. It is a good idea to get +45 and up to +55. Don't go too wide on the rims either - I personally wouldn't fit wider than 7.5" but lots of people have 8" too.
If you fit the wrong offset it can lead to all sorts of suspension or wheel bearing problems. It also changes the handling characteristics of the car.
Here is a wild +12 offset fit on the Euro (the person did this for fun)...
lolz ... love the pic ... definetely need a widebody job :P
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