Drawbacks of SEM
If you've found this post because you were searching for "drawbacks of sem" then I assume you want to know what the drawbacks of SEM are compared to the benefits of SEO. If I'm mistaken in that assumption please leave a comment so I can more accurately answer your question. I've also written a companion piece to this on the drawbacks of SEO so you may be interested in checking that out as well.
So what are the drawbacks of SEM? First of all, I hesitate to say there are any. If SEM works for you, then use it. If it doesn't, then don't. You don't have to decide whether SEO is better than SEM, you just need to figure out if SEM works for you. But that said, here are some ways to compare the two if that's what you're looking for.
1. SEM doesn't get as many clicks. Organic or natural search results get more clicks than pay per click ads, on average. Generally you're looking at 30-40% of the clicks going to PPC ads, and 60-70% going to organic search engine results. However, that ratio may be different for the specific keywords you want to rank for.
2. SEM is not free. SEM not only costs money but takes time. Some people think that it's easy to set up a PPC campaign and then you just let it go. On the contrary, even with a relatively small company that has modest SEM needs it's easy to spend 10-20 hours per week managing a PPC campaign for maxium effectiveness.
3. You pay to play. With SEM if you're not paying, you're not getting anything. If you get 100 clicks, you'll pay for 100 clicks. If you get 200 clicks, you'll pay twice as much. With SEO you pay the same amount whether you get 100 clicks or 1,000. However, this drawback to SEM is also one of its advantages. While you only get results when you pay for them, you only pay for the results you get.
I would recommend to almost all clients that they do both SEO and SEM. If they both provide positive results, why not? It doesn't have to be a choice between one or the other. You can run SEO and SEM campaigns simultaneously, and in fact there are some benefits and synergies to running both types of campaigns at the same time in terms of identifying valuable keywords and spotting trends.

