I suppose it depends upon the person. If you're one to worry about the 'what if's' constantly, then probably, getting a glimpse at your future self possibilities may not be a good idea.
You can already predict your future with 100% certainty. Life has a 100% mortality rate; although I'm not averse to the idea we might one day halt cellular senescence- perhaps immortal (barring accidental death) human beings have already been born.
Anyway, going back to gene testing- there are genes with high penetrance, and then those that are linked to a varying degrees of risks (some of which may only be slightly more than the general population). So if you look at a company like deCode, which make kits to test various SNPs (single nucleotide polymorphisms)- most of those only give you a risk score for a certain disease. If you are more likely to get alzheimers, then you might want to have an advanced care directive in place whilst you still have the mental capacity to do so, or if you hare more likely to suffer heart disease- you might want to have closer monitoring- perhaps regular stress tests or CT coronary angiograms. That way if you find that your coronary arteries are getting narrow, you can do something about it before you have a heart attack. It doesn't follow you will get any of those conditions (they're only risk scores), but at least you might be able to do something about some of them.
Other conditions might have relatively high penetrance, or very high risks, like the BRCA mutations. Many women choose to have the drastic measure of prophylactic mastectomy, because they have such good odds of developing breast cancer.
I like the idea, but I think it needs to be backed up with good genetic counselling.