HQuakers

I did a search a came up with a little bit of info, but nothing to answer my question.

The past few times I went into the shop to get an oil change they asked me if I wanted to switch to a high-mileage oil. My car has almost 154,xxx miles on it, but I have never changed over. I believe I use plain ol' 5w-30 right now, which doesn't cost much. I think they told me the high-mileage oil costs more.

My question is...should I change over? What exactly am I paying for in the different oil and can I expect anything bad to happen since I haven't been using it ever? I read on here that it helps condition the seals and clean the engine?

Thank you in advance for any help.