Well taking any steroids at all poses a risk, even half a gram (albeit fairly limited risk).
All he's doing is increasing his gains by increasing the risks (though it sounds unlikely that he's weighed this up sensibly).
He might be fine - lots of people run monster doses for long periods with no problems and the 1-2g ballpark is far from monster. But who knows. Most people will start to get some sides with what he's using.
A main issue is what he's going to have to do next. If it's his first cycle, presumably he's not massive, and if he's already on 1g test plus deca plus dbol, presumably he's knocking on the door of 2g in total a week. If this is in a 180-200lb guy, how much is he going to have to use to get to 240/260/+, assuming that's his aim. Always, always, for the love of god, run the minimum you need to make gains. You (he) will almost always have to use more next time - so leave headroom.
Then there's recovery. If he does plan on coming off, if he hasn't figured out how to recover from a half gram cycle, he's going to struggle on higher doses.
Most likely he's just going to get some sides which may or may put him off - be it gyno, acne, crashing when trying to recover etc.
He may have evaluated the pros and cons of upping the dose and decided his goals are worth it of course.
At the end of the day, he's probably going to have to find out the hard way.