I know strictly speaking you should try to get them in, as they are there to ensure that your diet is balanced with enough fibre and calcium.
I rarely eat my HE's as snacks, I usually incorporate them into my meals, but some days I just don't get them fitted in, and I'm not going to eat something 'just for the sake of it' so I leave them out - but I try to plan my meals so that this doesn't happen too often, because they are there for my benefit