Being a self employed person, I find this entire practice has had an impact on people running real companies with more than one client.
If you are going to work for a single client on any length of contract, get employed by them, enjoy the perks of employment, holiday, sick pay and so on. If you're going to be self employed enjoy the perks, ie a very slight tax advantage but also enjoy the negatives, no holiday, no sick pay and if you don't find yourself work, no money at all.
Worse still running a company, taking the risk of not finding enough work to pay the bills used to have a small advantage that dividends were slightly more tax efficient, now even that has been eroded because of this modern practice. Equally someone running a real company goes on to employ people as they expand.
These sole director, single client companies just take and give very little and now they're all crying over IR35 tests as well as employers looking for a no strings attached skilled person.