Although fading in the secularized West, mass intentions are a major source of funding for priests who receive insufficient financial support from bishops in poor dioceses. Catholic priests are required to note mass stipends they have received, using books like the one pictured above. 
Earlier, they were a part of every priest's routine, as the following document from 1925 shows. It is a report on how many mass stipends a missionary group distributed in 1925. Catholics would order mass intentions, give the money to the church group in the USA, and that group would then distribute the stipends internationally. As a result, the priests who celebrated the masses had to keep a record of the masses they said. 

Such records are immensely valuable historical sources because they show where each priest was on each day, and the altar where he said mass, as explained here.

Idealized portrayals of monastic cells like this one (note the candle burning, above) do not reflect the reality of monastic history. "The term cell is something of a misnomer for these conventual dwellings, as they were not simply single-room constructions," writes Kathryn Santner about Peruvian nuns in the Early Modern period. "[...] they formed an extended network of small houses composed of multiple bedrooms, sitting rooms, servants’ quarters, kitchens, and outdoor patios. [...] a cell built at Lima’s monastery of Santa Catalina in 1638 included a reception room, alcove, oratory, kitchen, patio, chicken coops, balcony, and staircase to the roof. [...] Employing the same materials and construction methods used in secular buildings, these lavish cells had the kinds of amenities and fine detailing seen in Lima’s stately homes, including upper stories," Kathryn Santner, "Money and a Room of One’s Own." Journal of the Society of Architectural Historians 81.4 (2022) 441-455, at 442.

The Hieronymite nun Juana Inés de la Cruz had in her cell: thousands of books, scientific and musical instruments, paintings, and curiosities. See Octavio Paz, Sor Juana, or, The Traps of Faith, trans. Margaret Sayers Peden (Belknap Press 1988) 247–248, qtd in Santner.

This etching of St. Simeon the Hermit in his tenth-century cell is idealized but at least shows a number of paintings and even more modern books.