I'd say good airmanship. Plus they may give you extra traffic info you may not have got otherwise. I find the MIL controllers in the S of England particularly helpful and sharp.
That stretch along the M4 around Newbury-Reading-Oxford is absolutely buzzing with traffic during the week at all levels (all potentially different freqs and some on none at all) and I feel a lot better having someone with a decent radar to talk to, no matter whether I'm in the MATZ or not.