SEO vs SEM
SEM: Search Engine Marketing – using search engines to market/promote the website (e.g. Google Adwords, sponsored linked, etc). You pay to have yoursite listed on search engines through their various promotions, and you may have to pay for each user the search engines send your way.
If SEO is working as intended, then there may not be a need for a SEM campaign; where as you will still need an SEO strategy even if SEM is working for you. SEM has a higher running cost and the cost is directly proportional to the number of users sent or the position of your ad.
SEO and SEM are usually best serviced by the same provider because they have already performed the research, have extensive consultation with you, and know which strategy is best for the task at hand.
SEM, in most cases, can be implemented in realtime and results are
immediate. Hence, if traffic is essential to your website and you’re still waiting for the SEO results, a short term SEM campaign may provide you with the traffic while waiting for your SEO to come through.