I know that documents and images embedded in them should be converted to CMYK before printing. Recently out of curiosity I printed both the RGB and the CMYK version of a photo (the CMYK version painstakingly tweaked to look as close to the original as possible) on a regular office printer. To my surprise the RGB file's print turned out to be noticeably brighter and closer to what appeared on the screen compared to the CMYK file's print.
I regularly volunteer as a graphic designer for small charity organisations who print their posters on their common office printers. Would it be worth to leave the PDF files I send them as RGB, and trust the printing machines to convert the colours to the best of their ability, or should I stick with what I learnt, and keep converting everything to CMYK?
Most regular office or home inkjet printers expect RGB files. If you send them a CMYK file, they will convert it to RGB then back to whatever internal flavour of CMYK they use for printing. This of course all depends on the printer drivers, settings, color profiles used, specific printer etc.
If you know for certain that these files are going to printed in-house using a regular office inkjet printer you're probably better off sending RGB files.
You usually only really need to worry about CMYK if you are preparing your files on a commercial print press (with few exceptions) . Most office printers are designed to work with RGB, Also some photo prints have more than 4 inks, giving them a wider color gamut than CMYK. So if you convert your file to CMYK before you send it to a photo printer with more than 4 inks, your just limiting what you can reproduce