It feels like such an obvious thing to say: self care is important, in general, and also in witchcraft, for so many reasons.
There is often a deep seated (inherited?) notion that caring for yourself, let alone loving yourself, is somehow wrong, too egocentric, and that you should always put others first. Others might struggle with their sense of self worth and feel they don’t deserve to be loved and cared for, that they are too fat, too thin, too out-there, too ugly and so on.
You might be reminded of the old “you can’t pour from an empty cup” saying and there is a lot of truth in that. If you are familiar with Reiki you will have been taught that this treatment is facilitated by channelling universal energy, not by depleting your own resources. It’s an important distinction.
Magic often works a lot better if you truly know yourself, warts and all. It helps to become aware of unconscious biases which might otherwise creep into your spellwork and distort or weaken the intended outcome. A very helpful book in this context is Vivianne Crowley’s “Your Dark Side” which has great pointers for recognising and befriending your Shadow.
Self care has several dimensions, for instance emotional (e.g. managing your stress levels), spiritual (maybe more broadly fostering a sense of connection), social (those all important boundaries, eh) but also physical: care for that body of yours, it’s the only one you’ve got and it serves you day in day out as best as it can. The more aware you are of your own energetic state from all of these perspectives, the better you will be at moving energy around more generally, and that in turn is an important factor in working magic.