DVT is in the business to supply low-cost labour to companies. If you ever outgrow your role, DVT will not help you properly evaluate your skills and see how you have grow and where you want to go. If you do well, you don't know. If you suck, you don't know. DVT can push your salary expectations down and make a lot of money from the client - that way they keep the difference. And, heaven forbid, you produce more than expected value - DVT will not help you get rewarded for your skills and talents. If your skills would ordinarily charge more money, DVT will discourage your practicing those skills at the client. If they don't get to charge for extra skills, you don't get to be the best version you can be at the job.
When you ask for a long-overdue raise, bad feedback comes out of thin air to cheat you out of a performance bonus.
You really should go in with a plan to leave as soon as a client engagement is over, go to interviews and measure yourself in the market. That way you'll grow.
Also, you don't get benefits like medical aid or retirement. The company just doesn't seem to care about it's people.
