Are deep conditioning treatments at a salon worth it?

I’m getting my hair done today at a high end salon. My hair is pretty long. About half way down my back. I want to grow it out really really long so I was thinking about getting the dead ends trimmed off, about 3-4 inches. I also told them I might get a deep conditioning thing done but I don’t know if it’s worth it or not. I’ve sort of been reading and it sounds like it isn’t. I considered asking the stylist but I sort of think they might just lie to sell it to me anyway so I wanted some advice here about whether or not to get it.