I find it useful.
People shouldn't be using it to justify bad behaviour from a partner, but to deepen their understand of them.
So if my husband's primary language was gifts of service but mine wasn't, I might not realise that him blitzing the house whilst I'm out was done out of love. So it means I can appreciate it more and thank him.
It also helps me understand why he might get grumpier than me if I leave my socks on the floor and don't do the washing up. So I make an effort to do so out of love.
Equally, because he knows that's not my primary language, he should realise that I'm messy because I'm a slob, not because I don't love him. But because my primary language is words if affirmation, he makes a mental note to tell me that he loves me frequently, even though it doesn't become naturally to him.
Physical touch doesn't have to be about sex and no one should be giving more than they want in that or any context. If you can't justify the money don't buy a gift. If you're tired don't do acts of service, if you're not in the mood for sex, don't. But gaining an understanding of how you and someone else loves is surely a good thing.
My issue is that I'm pretty balanced on all of them 😂. Totally greedy.