As far as larger files are concerned, that is as of yet not possible due to limitations on the blocksize(and if a post fails for this or any other reason the user doesnt see a lot about what happened). Should be able to adress this soon, say 14 days tops. Its surely not suited for data in the range of multiple megabytes without ridiculous amounts of steempower. But thats more than enough for plenty of important information or art to be secured.
