I am wondering if there is a scaling relation between the size of a grant and the administrative overhead/workload associated with it. My limited experience is that the relevant exponent is much less than one.
Small grants (especially travel grants of a few thousand $) seem to require comparable administration (pages of application, contract, memoranda of "understanding", special visas, progress reports, final reports, press releases, ....) as grants of several hundred thousand $. This administrative overhead is not just a burden on the scientist but wastes the money of the funding agency and university who are paying support staff to administer the grant.
Due to this large admin overhead I generally don't bother with small grants. However, I recently did successfully apply for one, partly for political and kudos reasons, and have been really struck by the problem.