You may find it difficult to market every product or area that you offer your services effectively through just one website. There are times when you may need to create a microsite for a particle product or area to allow you the best chance of ranking high on the search engines. Doing this will allow you to tailor all the content, images and Search Engine Optimisation on the site to be very specific to the product or service without comprising the look and feel or indeed rankings of the main website.
Many people link the navigation button off their current site to a mini 3 or 4-page site to allow an easy link between the two. If you are looking at doing this then speak to an online marketing agency that will be able to come up with a strategy as to how to create this, as if done incorrectly can have a negative effect.
If you use Google Adwords to advertise through then creating microsites can help improve your quality score on Google Adwords as you can link the ads through to a page that is highly relevant to what you are selling. Improving your quality score will not only often lead to a higher conversion rate but will often lower the cost you pay per click for each ad.