I carry several knives/tools as EDC buy my general preferred blade length is from at least 3" but usually 3.5" to 4".
I have been carrying knives since age 13.
I use my knives for typical things like cutting straps, cutting up boxes, opening packages, light gardening, cutting rope/twine, slicing fruit/vegetables, opening cans(multi-tool knives), scraping, etc. I also carry in case I become trapped in a burning car and the seatbelt gets stuck. Don't laugh; I know of at least one case where a woman was trapped in her car and could have easily escaped had she had a cutting tool to cut her stuck seatbelt; she ended up burning to death. Several construction workers also failed to get her out because oddly, not one of them had a knife either.
Jim