In the glossary of the CCC 2nd Edition, there is given a definition of mercy, which is as follows:
The loving kindness, compassion, or forbearance shown to one who offends.
In the Byzantine Church, the priest says "Let us pray to the Lord" (Господу помолимся) and we reply "Lord have mercy" (Господи помилуй, Κυριε ελεισον)
I find it rather interesting during the present pontificate we're speaking of Mercy. But in order for us to speak of it, we need to know what in the world that we're talking about, and whether an action in of itself is merciful.
The one thing I'd like to add to the definition of mercy that I've provided you is that mercy does not always imply kindness. In some situations we have to justly "be mean" in order to be merciful...
It is rather merciful to not allow a person to commit a mortal sin when receiving Communion in particular when this situation has gone public for everyone to know, and to receive would cause scandal amongst the Faithful. This is why the Church has CIC 915, not as a weapon, but rather as the greatest mercy she can provide to the Faithful, to help them not drown themselves further into the abyss. The same goes for the public knowledge of those that have re-married (Separation or Divorce does not exclude one from Communion per se)
At the same token it is merciful to allow people to present their case when they've been accused of a wrong doing. So of course it is positive as well. But Mercy can never be at the exemption of Truth.
Lord have mercy, we beg of Him to have compassion for our weakness...in His compassion for His creation, he gives us free will to serve Him...and so often we fail, and yet He still loves us...and in His mercy allows us another day.
Let us thank the Lord for His mercy, for without it, we're screwed.