Sans-serif v. serif for screen media
In the beginning of typography, all fonts were created to be used in printing. In this way, they were optimised to be as easy to read as possible on paper. One of the techniques used was to serif the letters, embelishing the ends to emphasise the shape. Now, however, typography also has applications on the screen, for example in websites, and choosing fonts that are easy to read is just as important as in printing.
To this extent, there are now both many serif and sans-serif fonts available electronically. However, not all of them are suitable for the screen, and this applies in particular to the serif fonts.
The main problem with using fonts designed for print on screen media is that, not being intended for use as such, they do not scale well, and at lower point sizes can appear quite blurred. This is due to a lack of hinting, that is, additional information encoded into the font that allows better display at smaller sizes. This hinting is not needed on printed material as the resolution is very high, but on screen it can be a big problem.
To solve this problem some companies have created serif fonts with hinting, such as Microsoft’s Georgia. In these case, it is fine to use the font, but remember that the legibility advantages of serif fonts are negated on-screen.
In the end, as long as you choose a font that displays fine at the size you choose for it (don’t forget to check on all platforms (e.g. browsers or operating systems) the design is intended for, they render fonts differently), and it looks nice, there is no problem.