Yes mainly when landing but they do tell sometimes if the airports vincinity is crowed..They mainly vector you around to put you in a "pattern"... If you want to see how is is really done do this..

go to Passurs website of Boston Logan
http://www4.passur.com/bos.html
and also go to LIVEATC.NET and scroll about half way down the page and click on Boston Approach/Departure you will here boston vectoring aircraft all around and you can see the aircaft doing these manuvers
http://liveatc.net/feedindex.php

I am a huge fan of the site..I would love to here some Europe chat..but "You" have certain restriction which limit ATC talk....

ATC in real life uses speed as a tool to maintain separation between aircraft, and it works quite well.  Just imagine in a busy terminal environment how difficult it would be to maintain a longitudinal separation of 5 miles if every aircraft was a different airspeeds.  Just like vertical, longitudinal and lateral separations, speed adjustment is a valuable tool available to controllers.

Are you complaining?  
Then try the new ATC simulator, partly developed by a very good friend of mine (same guy who wrote the guide below)

So far you can only assume the role of a controller at ESSA, but it's FREE and it's GREAT  
Official page
http://atc.flygsimulator.se/

Quick guide
http://www.fsnordic.net/discussion/index.php?board=16;action=display;threadid=32...

the arrival aircrafts are already flying on their assigned STARs (which are not assigned by you), but you must choose which runway they will land on

Edit: Of course you have to vector them and clear them for approach etc.
It's great fun though