Look, I like to roll dice. Its fun, especially in in-person games. But I hate all the arithmetic you have to do as a result – especially hit points, and especially when you have multiple sources of hit point boosts (eg temp hp, the spell Aid increasing your normal hp, and/or for example an arcane ward for abj wizards). So this does that for you.
Originally, I made this to make using Spell Points (as opposed to Spell Slots – see DMG pg 288) easier. So if youre using spell points in your campaign, thisll help with that. Otherwise it keeps track of spell slots, which is fine I guess.
Oh yeah, and it keeps track of some of your class features, like Metamagic Sorcery Points, Lay on Hands, Bardic Inspiration, Action Surge, Rages, and that sort of thing. That way when its been months since you last played in person (arg) you can have all your resources up to date.
Finally, if your DM has this app, they can host a game, and get the basics about your character (like passive perception, AC, and/or save DC). They can also keep track of initiative, which is nice.
Entering a character into the app is easy and quick, because it doesnt need everything – just your class levels, and some scores/feats to help calculate your natural HP, passive perception, and so on.
So look, this isnt going to allow you to completely run the game. It doesnt have every spell, item, and ability. But its free, you dont need to sign up for anything, and it helps keep track of the basics while leaving the rolling to you. Give it a shot!