Using .PHONY to suppress rebuilds of included makefile fragments

[J.T. Conklin]

A co-worker started adding .PHONY: targets for each included makefile
fragment.  For example, changing:

   include Foo.mk

to:

   .PHONY: Foo.mk
   include Foo.mk

arguing that this suppresses gmake from attempting to regenerate
Foo.mk using dozens of implicit rules, and therefore improving
performance.

I've never seen .PHONY used in this way, but from the gmake -d output
I see it indeed does what he claims.  Are there any reason why not to
use .PHONY this way?  Is there a better idiom to use to avoid rebuilds
of Makefile fragments.

Thanks in advance,

     --jtc

-- 
J.T. Conklin