It is very strategy dependant but is extremely useful and is typically underestimated by players, esp. at lower difficulties. It does happen to be slightly weaker at lower difficulties because AIs dont REX nearly as much but is still quite useful.
If I can achieve a faith generating pantheon on any peaceful victory game, my strategy is almost always the same:
1. Take PILGRIMAGE founder bonus
2. Take an enhancer bonus that increases the passive pressure (aka RT/IP or, in desperation, the -30% missionary cost or the doubled pressure to CSs)
3. Spend all or almost all of my faith from immediately after I enhanced the religion up until shortly before industrial to spread the religion starting with immediate CSs and neighbor civs that down have a religion yet (typically, unless they generated a lot of FPT, I let the external pressure convert my satellite cities).
What this leads to:
Around T150 when I pop into industrial era, pilgrimage accounts for 20-50 FPT for my empire and my overall pressure is large enough that it should stay around that level until the end of the game(on deity). So more or less, this strategy, allows me to purchase an extra 2-4 great people from faith that I wouldn't have had otherwise. On lower difficulties, having a strong outgoing pressure means most newly founded cities by the AI will get immediately converted and you will passively gain more and more benefits from your founder bonus as the game progresses.
It also contributes to my tourism to the civs sharing my religion if I go cultural, helps my diplomacy with some civs when their cities convert from raw pressure (as opposed from via missionary/prophet action) which can really only be achieved if you have multiple cities pressuring.
It is a little harder to dominate religion as it was in GnK. Back then, I've had OCC games on deity where I would convert 45-50 cities out of 55-60 cities on the map and get 100FPT from pilgrimage...
In GnK, warmongerers also typically needed the happiness gains from Ceremonial Burial. It was nerfed by half now so it's not nearly as potent I would probably use church property instead.
Last but least, an underestimated combo is to pair the +15 resting point with CSs+pledge+patronage policy and take the enhancer bonus that doubles the pressure to CSs. For so long as each CS is within 10 tiles of ~3 or so other CSs, you can probably "hold on" to most of those cities naturally because it is as though they would receive the pressure from 6 cities. This means any other completed quest will grant you an ally for a long time and that you could afford to withdraw a pledge if you were at risk of losing good relationship with an AI and still climb back to 35 resting points and receive the friendly benefits.
