there are alot of questions that need to be asked to help you out specifically, although if you look in yesterdays posts you could find a few topics with the exact same question.
mall crawler
If you dont do much wheeling and its a big bling bling truck, you can get away with just cutting the edges off the front fenders and no one will know the diffrence. this is what i did at first with my 36s, but i only had a 4 inch lift.
wheeler
If you do abunch of flexy stuff and your tires willl be thrashed into your sheet metal, i would deffinately trim a litte bit. currently i am running 7 inches of lift and i only did some minor trimming and i can get a decent flex. i even considerd bushwacker cutouts. but with the thousands of threads on ck5 with the question repeditaly asked, bushwacker cutouts, yey or ney, you will find alot of neys.
1. they break easy (someone said they broke one on a trash can coming out of a driveway)
2. they are expensive
3. IMO a clean fender trim that will cost you near to nothing will look better then getting bulky grey, expensive pieces of plastc.
John