US neutrality to the max (full adherence to US neutrality Acts) means:
1. Cash for all purchases, and the UK was running out of cash.
2. Maybe no destroyers for bases deal. The ships themselves were marginally useful but the US using those bases for patrols, even when neutral meant more eyes looking for U-Boats.
3. No US flagged vessels bringing cargoes to the UK. This puts more strain on UK shipping.
4. Limits on what the UK can buy from the USA. There were instances where, early on, to get around some of the restrictions you'd have things like aircraft flown to the US/Canada border then towed across the line rather than flown directly. This also means that because of the objections that some in the military and isolationists in Congress had to selling stuff to the UK that was originally planned for US rearmament some or all of those sales do not happen.
5. Limits or elimination of repairs/refitting of RN ships in US dockyards.
6. The neutrality zone, US escorting of convoys in the western half of the Atlantic is reduced or does not happen.
All of this is very bad for the UK.