"Cross-chaining" (whether it's using the big-big or small-small) has always been one of those things frowned upon by experienced cyclists. But more and more, component makers are saying their groupsets will allow this, despite the negative effects.
Click HERE for a great explanation of why you don't want to do it even if it IS possible!
Especially with the development of compact cranksets, "cross-chaining" has become popular, particularly in the case of "big-big". Beyond the negative effects described in the linked article, far too many (even pros!) ride along in the big ring (in this case 50 teeth, which is not so big) and change their gears solely in the rear, clicking up and down an 11-speed cassette, perhaps with a large cog of 29 or even 32 in some cases.
As the climb steepens, they'll continue working their way up to the largest (inner-most) cog, still in the big-ring solely using the rear derailleur until...
...they need a still lower ratio. What happens now? There is only ONE shift that can result in a lower ratio - shifting down to the small (usually 34) chainring. In some ways this is the equivalent of jamming your car into 1st gear at highway speeds. To equal this with a rear shift you'd go instantly from a 12 tooth cog in back up to a 28 with one single shift!
In addition to a way-too-big step, with the big-big combination the chain is maxed out with the most extreme spring tension from the rear derailleur. Suddenly, with this shift you release all that tension instantly. BAM! You push the chain off the big ring under all the torque of pedaling in a too-high gear combined with that spring tension and ...
..quite often, even to the pros, right after BAM! is the feeling of pedaling against no resistance (or worse, a jammed chain) as the chain falls inwards so violently it misses the small chainring and ends up around your bottom bracket shell, leaving you without any forward momentum. OOOooops!
At best (like the pros) you stop, dismount and manually pick the chain up and put it back on the chainring while at worst, the chain jams and you fall over!
Don't let this happen to you or your bicycle! Take the advice of the website and use your compact (or triple for that matter) the way it was designed to work by using the smaller cogs with the larger chainring and vice-versa, avoiding cross-chaining except in an emergency.