Q. 1. What is the purpose of the Communion paten?

A. 1. The Communion paten is a saucer-shaped plate usually gold or silver plated, similar to the Mass paten that accompanies the Chalice, but having a projecting handle.

Its purpose, held under the chin of the communicant, is to catch any particle of the Sacred Host that may fall. It was the common practice to use a Communion Paten prior to Vatican II in the Latin Rite when Communion was received on the tongue.

Since Vatican II, the reverence given to the Holy Eucharist has changed drastically. Communion is now given in the hands of the communicants. If the Sacred Host is dropped on the floor, someone picks it up, consumes it or it is destroyed by the priest according to Church regulations related to this matter.

Quoting from http://www.ipadre.net/2015/12/why-the-communion-paten/:

On 25 March 2004, Francis Cardinal Arinze, Prefect of the Congregation of Divine Worship and the Sacraments came out with Redemptionis Sacramentum. The document dealt with various issues and abuses related to the celebration of Mass.

Paragraph #93 reads:

The Communion-plate for the Communion of the faithful should be retained, so as to avoid the danger of the sacred host or some fragment of it falling. [180]

[180] is a footnote to the Missale Romanum, Institutio Generalis, n. 118.

The General Instruction of the Roman Missal reads:

118. The following are also to be prepared:

3. On the credence table: the chalice, a corporal, a purificator, and, if appropriate, the pall; the paten and, if needed, ciboria; bread for the Communion of the priest who presides, the deacon, the ministers, and the people; cruets containing the wine and the water, unless all of these are presented by the faithful in procession at the Offertory; the vessel of water to be blessed, if the asperges occurs; the Communion-plate for the Communion of the faithful; and whatever is needed for the washing of hands.