Secret Squirrel...
Well, my "colleagues" have rather forcefully answered, and here's my own 2p's worth.
Yes, you or your box of tricks can probably fly down the track very well, but their are other aeroplanes out there who either have drivers that can't fly as well as you or have autopilot's that ain't quite so clever.
In ATC we are required to ensure separation between you and everybody else, and since we can't rely on everybody else, radar headings are required. It also gives us some measure of control over the rapidly changing dynamic situation in which we NEED to provide 5 miles/1000ft separation.
The reason for all the little heading adjustments? Could be lots of reasons. The wind (as mentioned above), other people not flying headings very well, and a whole host of other things. You're operating in a busy environment, in the UK there is more climbing / descending traffic vs. cruising traffic than anywhere else in EUR. Something else to consider is a/c performance. The "Greenway" is often populated by rather speedy B747s who will run down your 146/RJ very rapidly... consider, 5 degree hdg change for 10 mins, well you do the maths!
I hope this helps. Try to understand however that ATC is being pushed harder than EVER this year. We don't have much in the way of resources at LATCC and operational ATCO's are getting somewhat jaded, while still trying to provide the best service they can. I hope this explains the replies above.
Please come and visit LATCC sometime. The phone number is on the back page of the latest FEEDBACK. I promise you WILL be made very, very welcome and you will learn something.
Rgds BEX