Should we use v-model to modify Vuex store?

Above solution can also implemented with mutations:

<template>
  <input v-model="message">
</template>

<script>
import { mapMutations, mapState } from 'vuex';

export default {
  computed: {
    ...mapState({messageFromStore: 'message'}),
    message: {
      get() {
        return this.messageFromStore;
      },
      set(value) {
        this.updateMessage(value);
      }
    }
  },
  methods: {
    ...mapMutations('updateMessage')
  }
};
</script>

I think another good option which hasn't been mentioned in any answer here is to use vuex-map-fields. In fact, the library author has written a very nice explanation for the library's usefulness. As per its GitHub page, to use the library you can do something like this:

In your Vuex Store, you can have a snippet similar to this:

import Vue from 'vue';
import Vuex from 'vuex';

import { getField, updateField } from 'vuex-map-fields';

Vue.use(Vuex);

export default new Vuex.Store({
  // ...
  modules: {
    fooModule: {
      namespaced: true,
      state: {
        foo: '',
      },
      getters: {
        getField,
      },
      mutations: {
        updateField,
      },
    },
  },
});

And in your component code, you can have something along the lines of this:

<template>
  <div id="app">
    <input v-model="foo">
  </div>
</template>

<script>
import { mapFields } from 'vuex-map-fields';

export default {
  computed: {
    // `fooModule` is the name of the Vuex module.
    ...mapFields('fooModule', ['foo']),
  },
};
</script>

Additional examples for various use cases are shown in the library's GitHub repository that I linked to in the first sentence of this answer.

https://vuex.vuejs.org/guide/forms.html

When using Vuex in strict mode, it could be a bit tricky to use v-model on a piece of state that belongs to Vuex.

The "Vuex way" to deal with it is binding the <input>'s value and call an action on the input or change event.

Be sure to check out the simple "Two-way Computed Property" example on that page:

<input v-model="message">

computed: {
  message: {
    get () {
      return this.$store.state.obj.message
    },
    set (value) {
      this.$store.commit('updateMessage', value)
    }
  }
}