A weed is only a plant in the wrong place. I tend to pull up the ugly looking ones and leave the attractive ones.Of course beauty is in the eye of the beholder but generally speaking cultivated plants tend to be the ones we have all decided are nicer to look at! There are exceptions. Best thing to do is...if you like it leave it alone.Happy gardening.
I quite agree that if you are happy with the plant to leave it alone - but it's also a good idea to know the names of your 'visitors'.- knowing their likes and dislikes, poisonous or not - so I would get a copy of Dr.D.G.Hessayon Flower Expert and any Wild Flower guide so you can decide who stays or goes. A library will have all you need if you don't want to buy or borrow.