If its not to bad and soon disapears and it drives OK I wouldn't worry about it. most repair work is expensive now which is why I still do my own. Your problem is likely down valve guide/seal wear and is not serious.

If the engine runs unevenly while its smoking it could be down on one cylinder which may need attention but if its smooth leave it alone.

Is it dangerous and damaging ? Any ideas on cost ?

Your habit of driving off the instant the engine fires is defo damaging. It's damaging the valve stems and guides and quite possibly the turbo bearings too (and maybe other areas). Both these areas are big bucks if the damage becomes severe and in need of remedial action.

So, first thing is to get out of that habit. How I do that is to get in, start up, then put on my belt, then drive off. the time taken to put on the belt allows the engine oil to get going. Another thing you can do is fit oil with one lower rating on the cold rating (eg 10W40 spec'd so fit 5W40 and make it fully synthetic)

How far has the damage gone? Does the blue smoke last a few seconds and then it's gone? If so the damage is likely to be light and if you observe the above may not progress further. Do you get blue smoke coming out the exhaust if you lift off at speed? If so then the damage is more severe and may need attention. What was the HC reading at the last MoT?