Sacrament isn’t worth leveling for your Last Rites in terms of damages.
Note that I haven’t checked recently, but normally leveling your Aspersion increases your Aspergillum quite a bit, making it worth maxing (or at least leveling) if you have the extra points.
They’re worth casting if you have them - even if it’s only for yourself - since the shop versions are decreased by 30%, but they’re not mandatory if you don’t plan to focus on being a support since now all buffs can be bought and last for over 40 minutes.
And like the others said, you can just go full INT since others will always buy buffs, and just don’t bother leveling/maxing the buffs.