It can be used to maximise healing from resting, if your characters can coordinate it.
Hit Points (PHB 196, bolded for emphasis):
Hit points represent a combination of physical and mental durability,
the will to live, and luck.[...] This number changes frequently as a
creature takes damage or receives healing.
Receiving hit points is healing.
Resting (PHB 186):
If the rest is interrupted by a period of strenuous activity—at least
1 hour of walking, fighting, casting spells, or similar adventuring
activity— the characters must begin the rest again to gain any benefit from it.
At the end
The character regains hit points equal to the total.
So resting is healing, and Beacon of Hope does not interrupt the long resting of the party.
For the duration, each target [..] regains the maximum number of hit
points possible from any healing.
So Beacon of Hope can be used to maximize the hit dice healing for the resting of the party during a long rest for all members.
For the Short Rest only the other party members can benefit from the maximised healing. As the cleric would be casting a spell, and a single spell is strenuous enough (compare to the 1-hour leeway of Long Rests):
a character does nothing more strenuous than eating, drinking,
reading, and tending to wounds.
Confirmed in the SAC V. 2.5 P. 10:
Does casting a spell while taking a short rest in-terrupt the rest? Yes. Spellcasting is more strenuous than the activities listed
on page 186 of the Player’s Handbook: “eating, drinking, reading, and
tending to wounds.”
Do mind, though, that this takes a form of coordination of time that not every DM would rule as feasible or plausible due to the necessarily required understanding from a character point of view and their knowledge about the (mechanics of the) world.