Getting off topic now, but the most prominent reasons it is bad to share an iCloud account from my perspective:
- It messes up Apple Music; you can't have two subscriptions on one Apple ID (without Family Sharing) so if you and your partner want to both listen to Apple Music at the same time, you can't. Even if you don't want this today, you may do in the future - by which time unravelling your accounts is nigh-on impossible.
- If you're Apple-o-holics, sharing an account limits you to five devices each (which I and my partner would easily exhaust... )
- You don't get separate email addresses.
- Your contacts, calendars, reminders, photos, and so on become merged. While someone of @Weaselboy's technical literacy would have little issue separating these into lists/albums/whatever, the user who shares an iCloud account tends to be novice and unfamiliar with this.
- In the unfortunate but common instance of a break-up, you can't easily split your content and you can each activation lock each other's devices...
Like anything, it's doable but vary rarely is it a good idea.
Also, re Apple Maps, this might be okay
today but is an example how future software features are designed around the principle that one iCloud account = one person, thus you might be locking yourself out of future features.