Section 111 is not the general catch-all many people assume it to be. The devil's in the detail. Breaking it down, it gives the council the power to do anything which:-
will facilitate the discharge of any of their functions; or
is conducive to the discharge of any of their functions; or
is incidental to the discharge of any of their functions.
In order to use this power, the council must first identify which of their functions the proposed expenditure relates to. In almost every case, if the expenditure relates to a function of the council, it will have a specific power to incur the expenditure, so Section 111 is not the appropriate power to use. Legitimate use of S111 by parish and town councils is extremely rare.
Your example of a clerk regularly using Section 111 for expenditure that didn't fit under the normal powers seems at odds with the legislation. If the council lacks the normal power to act, S111 will not provide it. If that were the case, Section 111, handed out freely to every council since 1972, would be of far greater value than the General Power of Competence and no council, councillor or clerk could ever be accused of acting ultra vires.