SEO gets traffic to your website organically and without using paid strategies. It’s not an instantaneous solution to increase website traffic and will take at least 3-6 months before you start witnessing some tangible results. If the competitiveness of your industry is high, it may even take longer than 6 months for ranking on traffic-heavy keywords.
SEM on the other hand, uses paid search strategy to instantaneously increase website traffic and conversions for your brand. So, depending on your marketing objectives, you can grow sustain-ably using SEO or invest in SEM to build traffic instantly.