Certain professions; Legal/Software/IT Services/Accounting; make it very easy for one or group of employees, to just take a company's current clients, offer them a low price, and start a new firm thereby causing losses for the original service company. Business which got burnt by their employees starting competitive business thereby started adding these clauses into their agreements.
Sometimes competitors itself would poach key employee which is working for a Client X thereby gaining an edge and thats why the clause for 'Client'.
It's much easier for a Company to let a potential employee go then position themselves to a losing client situation.
Also Most software engineers when they leave the company take backup of not only the entire code they've written but also the entire code for the project they've been working on. Thats why the IP Protection clause.
Again, your blog content would be different if you stopped being a Computer Scientist and started your own Company.