A way of supposedly increasing the conversions from your site is by adding calls to action, links or banners or buttons nudging people away from simply reading and towards taking action - purchasing your products, enquiring about your services and so on.
The practice of including calls to action is taken straight out of the advertising industry. Advertisers have a small list of things that they need to include in an advert, and a call to action is on that list. However a website is not an advert. Users browsing the web are mainly in a mode where they will read and compare and research a purchase. Who would click the first "buy this now" button they see when they can hop onto another site and check out alternatives and price first? In this context, calls to action may not be very effective and can be intrusive. It's even less effective if your call to action is not something as passive and easily handled over the web as just "buying", such as "Enquire now about our calibration service".
In the UK we also like our calls to action implicit. Watch TV ads for a few minutes and the number you'll see that include an explicit call like "Sofas half price at DFS until Monday! Come down to DFS showrooms today!" are small compared to the number that run more along the lines of "The sun is shining and this man in trendy clothes is laughing with a group of attractive women. What's that he's drinking? Oh, Coca-cola."
So include calls to action, make sure they are seen, but keep them understated and out of people's faces and users may find your site that much more appealing - easily enough to outweigh the effectiveness of intrusive calls to action.