This question has got a dual perspective –
1. A Personal Perspective:
Do you need to blog because you like to write and a blog is the best canvas where the thoughts and ideas can be poured on and made to reach out globally?
2. From the Business perspective of your website :
Do you want to reach out to your visitors and clients with more and more information about the company services, products and other developments? Does your website need additional content?
If you have a ‘YES’ for an answer for atleast one of the above questions then yes, you surely need a blog.
If you want a blog from a personal point of view or the business point of view, you surely need to decide the frequency with which you need to update the blog. There is no point on starting a blog and not updating it.
If you have a website then a blog surely is a source of adding valuable content for the site which in turn surely helps in improving the rankings in the search engines. But, the blog has to be focused, well maintained and also updated daily.
Many times I always argue with myself and come to the conclusion that quality is better than quantity and it is ok if you do not update it daily, but then from the hard core SEO perspective truly speaking both the quantity and quality both are important and necessary.
Yes, if you have a blog do not compromise on the quantity or the quality and eventually you not only benefit from the search engines but also carve a niche of your own and establish a unique identity on the web by your own very individual style of writing and presenting your thoughts and opinions on the related topics.
Daily updation ensures regular visitors, on the other hand if you reduce the frequency it may be an out of sight out of mind case from the visitor point of view and affected rankings from the search engine side. Blog articles today have the tendency to get indexed as soon as they are published. So if your blog offers fresh content daily your site definitely gets preference from the netizens and the search engine bots.