For any rolls, for Journeys or otherwise, I follow 2 principles: (1) the principle outlined in the book, "You are allowed to push rolls even after a successful roll, but only if rolling additional SUCCESSES will increase the effect of the roll in some way." [p.44 Player's Handbook] and (2) unless there are risks associated with failure and rewards associated with success, I don't ask for a roll (with rare exceptions). Pushing to LEAD THE WAY isn't going to help if they already have 1 or more successes, for example, but it will help if they have none; further, they need to get where they're going and want to do so without risking potentially damaging complications from mishaps.
I've found both as a player and now GM in this system that any attempts at farming (most commonly attempted with Journeys rolls) can rapidly come back to bite them during Random Encounters and other dangers without the GM needing to actively try to discourage them.
As an example: Recently the party stayed around camp for an entire day, HUNTING, FORAGING, etc., gaining some WP and damage from pushed rolls. As they weren't HIKING, I only rolled once for an encounter and even rolled randomly to see when it occurred, a nearly deadly random encounter with the Blood Mist cascaded into a series of events that, within 3 Quarter Days killed 3 of 4 of them, all of which had plenty of food, water, and WP remaining, mainly because they were all damaged from pushing rolls when well-stocked, were many hexes away from the nearest friendly village, and had made enemies of local wolfkin.
If pushing rolls too often is grinding things to a halt and interfering with the GM and party's enjoyment, more power to disallowing pushing for certain rolls or skipping them entirely, but I think that as-written any attempts at farming are themselves potentially dangerous, WP caps out at 10 anyway (if I'm not mistaken), and uses of WP can save lives and achieve goals but rarely on their own.
TLDR, in my experience the danger of WP-farming is easy to underestimate (players) or underplay (GMs), and WP itself is valuable but easily overvalued.