Here's a question from a beginner. If it already has a discussion somewhere, I would appreciate a link.
Why would I want to play on Steam rather than my PC?
Steam is not really the question of "to play on Steam" versus "to play on my PC" - both play on your PC (Windows or Mac), Steam just adds another "layer" / client application which serves different purposes:
1. Steam started as a simple game store where you could buy digital versions of games (no way to get a CD or DVD from them)
2. Steam also acts as a DRM (digital rights management) system that ties a game to your (Steam) account, verifying your right to own/play the game. There is no way for you to give the game to another person or resell the game
3. Steam requires an online connection to download and install a game but it does NOT require you to be online every time you play (there is an offline mode but I think there is some online verification from time to time, but I'm not sure about this. I have NEVER run into any issues with this (but granted, I'm basically online all the time on all my devices)
Some advantages that Steam offer:
4. Many games these days are ONLY available on Steam, that, of course, does NOT apply to Matrix Games/Slitherine games
5. Steam automatically applies patches and updates (if you are online) to games and therefore making the whole install & upkeep process really a one-click affair
6. For many games, Steam offers "cloud" saves, meaning your save games are stored in the cloud. While this protects your save games from problems with your local PC, it also ...
7. ... is great if you game on more than one machine. You can install the Steam on many machines and you have access to your cloud saves on each machine.
8. Steam offers good to great saves on many games basic all the time (again, not so much a factor with Matrix Games/Slitherine)
9. Steam has it's own system/repository for modifications (mods) for many games (not Matrix Games/Slitherine, as far as I know), making it easy to select, install, and maintain mods for games
10. There are also a couple of other features, such as matchmaking for online/MP games, screenshot, streaming, chat functionality etc.
There are also issues with Steam:
10. Some people have reported issues with the technical side of Steam; I'm using it for years now and have A LOT of games on Steam and do all my gaming through Steam and never had any issues but then again, not all systems are alike
11. If Steam should go down/bankrupt, it's at least high questionable what would happen to your games, since you have no way of downloading complete installers or get CDs, if the system does not exist anymore, all the content may be gone, too - that's basically the issue with every cloud system today.
I think Matrix Games offers are great middle-ground: I buy all my games from them directly to support them (Steam takes a rather steep percentage of the sale price from the publisher) and they give you your own download AND a Steam key and you therefore have both options. I play all my Matrix Games games through Steam these days though (to the extend supported).
Steam itself is free, so you can give it a try