We use the monitor more during the day. At night, Gabby's room is right next to ours so we hear her when she cries. The only time I use the monitor at night is when the weather is warm and we need a fan on us to sleep. Then I can't hear her so I have to plug the monitor in. I find it annoying though because she sometimes cries out but puts herself back to sleep straight away. Normally I don't hear those little cries but, because of the monitor, it wakes me up. I've run in to her room a couple of times only to find a sleeping baby, LOL. I now know to wait a minute before I run in.
We use the monitor during the day because our office is out in the garage so I can't hear her if I am on the computer. It's also difficult to hear over the TV in the living room so I like to have the monitor on even when I am inside (and even though our house is pretty tiny).
We have an anglecare one that we borrowed from friends. They are due to have another baby soon so I imagine they will want it back. I'll have to buy one but I definitely won't get the same one. I want one of those ones that switches on when there is a sound - not one that has the sound going the whole time. Also, we find we get a lot of interference with the anglecare one.