What determines what you put in your ad is where you are placing it and the message you want to convey. It is therefore not a clear-cut thing to simply say put a little information or plenty of information. If you are advertising online particularly on free sites, you are severely restricted to the number of words the site will admit from you. That clearly determines the amount of information you can provide. You may not really have much of a choice about how much information you can provide because of these restrictions. What really matters is be sure that your message is captivating enough and conveys all the information you want to put across no matter how short the message is.
Any and every ad is designed to grab as much attention as possible. If you use pictures or banners, you need fewer words to grab maximum attention because of the pictorial effects of pictures/banners. Even if you use test ads, the fewer the words the better for attention-grabbing purposes. Most people look at ads and from the images they are attracted to take a closer look. The attention span of many people is also very short. For such people, the smaller the ad information, the better.
All told, I believe it is better to provide less information in your ads for reasons adduced above. That is what is more result-oriented and most effective.
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