I have a bunch of 8oz plastic squeeze bottles. They are filled with paints and mediums that come from unwieldy jars. I label them, although sometimes that's not enough like when I grabbed white gesso thinking it was matte medium. Surprise!
I work pretty fast, and I find the idea of putting down my paint brush, using both hands to open a jar, and then somehow transferring that jar's insides to a palette really cumbersome. (Also messy.) Doing the squeeze bottle transfer every couple of weeks (or months) makes life a lot easier. Sometimes the tips get clogged, but it's worth the cleaning time for the time spent not frustrated about jars.
For getting mediums/paints from jars into tall bottles, it's good to have one. At first you'll think, "Oh no. My aim is just fine." If you find yourself thinking that, at least allow yourself a piece of plastic under your aim. I'll report back on how important it is to have one funnel for clear mediums (matte medium, self level gel, etc) and one for dark colors (like black gesso.) Also, when pouring through that funnel, work in small batches. That is unless you are really really good at translating funnel volume to squeeze bottle volume. I, as it turns out, am not.
Used Up Paint Bottles:
I paint with two types of soft bodied paint: expensive Golden paints and much less expensive craft paints. While I was bemoaning the fact I hadn't purchased more 2oz squeeze bottles at Dick Blick to make glazes, I realized I had a bunch of bottles all ready at my disposal. I just found my craft 2oz paint bottles that were almost empty and added matte medium (or white gesso that time I wasn't paying attention) and suddenly I have access to all those glazes!
Image Note: I put a G on the tops and bottoms of paints I've turned into glazes. The colors inside never match the color that has been stained onto the plastic. I always forget this simple fact.