The issue is that when the Central Bank buys dollars, it is effectively being financed by companies taking on more debt in dollars. This makes those companies very vulnerable if the exchange rate moves. In my opinion, keeping the dollar artificially cheap discourages private investment and hurts job creation.
It is a good explanation in that Ambito article. It is educational. All of this is complex to understand. The formation of liquid reserves is done at the cost of interest from the bonds issued, which seems like the debt keeps increasing.