Nice topic
If they are really mini sheets, meaning they can stay on a 12x18 envelope leaving space for address, and it is easily available its FD mark or a special cancellation, generally I collect them CTO or sent if I receive from another people.
Otherwise, I collect them mint.
Here in Italy no stamp or minisheet is sold inside a package, they pick up them from a big book with cardboard pages, where they simply lean on.
From my collection I like many , but to make some examples:
2018 minisheet of UN Vienna issued for a stamp fair in Verona, Italy
Those are the last three miniature sheets that were issued by Cyprus Postal Services. Nature and history. I collect them on First Day Covers. This combination of a miniature sheet on an envelope with the postmark and the extra artistic detail is something that I like a lot.
I collect them to use on envelopes, especially the older ones that are less than a letter rate in Britain. For example I have about 50 of these two sheets from the 1980 Stamp Exhibition in London. Perfect for sprucing up a plain white envelope with some other stamps.
Our minisheets are usually too big and too overpriced to be on postcards. Postage rate for postcards is currently only 80 cents worldwide but our minisheets are usually at least $2 and above.
I usually collect minisheets and the lowest value is $1 which is no longer in print.