Do fish need a place to hide?

[SkyesRingo]

My mom and I have a 20gal tank with guppies, 3 goldfish, and one of those plecostimus (? Cleaner fish). She recently just took out the large hollow log decoration that has been in there for a year, and says they don't need it. All that's in there now is a fake plant and a bubbler. I say they need it so the guppies can escape the big goldfish, and so Mr. P has a place to hide as Well. She says she's going to get some smaller decorations but until then won't put the log back in. So is it okay for the log to be out? And not have a place to hide?