Unfortunately, I am still a fan of "paper" and I have a vast library at home... including duplicates because perhaps one edition makes for beautiful books (in my opinion), like the 4 volumes of Carish's 'Mille Canzoni', but they are cumbersome to carry in a bag, so I have duplicates where there are the usual pieces but in an A4 format that is easier to carry.... Well-made sheet music which, along with many other volumes, has been very useful to me when I needed the structure with chords to write an arrangement without always having to transcribe, also because for processing instrumental parts, including reharmonizations, it is extremely convenient to have the melody right in front of you. For these reasons, and also simply because I like buying a book every now and then, I am overflowing. I start from this archive to create the arrangements that I need from time to time. From what I see, sheet music already written for piano is ugly, approximate, often just wrong, with those big, clumsy chords that say nothing and actually sound bad in the end.
I advise the friend who opened the 3D to look for all the pieces he likes, but to do a full immersion of study as soon as possible to create his own arrangements or to eventually improve his ability to "develop" an arrangement extemporaneously starting from reading melody with chords. For work, I specifically prefer sheet music with melody and chords, preferably well-laid out without absurd page turns, so that among dozens and dozens of songs to play, there is the minimum amount of information to read, leaving room for spontaneous creativity. With a little effort, you quickly reach the point of arranging a song "on the fly." After all, to make a melody + chords sheet music "sound," in an initial phase, it's not necessary to do anything too complicated!