Should I use a full node as my main wallet? A few days ago I decided to download Bitcoin Core so I can use it as full node, to help the network and also as my main wallet. 

Since then I keep reading a lot of people saying that you shouldn't use a full node as your wallet but I can't figure out why. 

Is there any good reason not to do this?
The only reasons are the syncing time and storage requirement (which can be lowered from about 200GB to 1GB by pruning). A week or so to sync first, then depending on how often you use it, it'll take a some minutes sync. These are major pain in the ass and because of these I would put it into the category of "good reason to not use as a personal wallet". I would definitely not suggest this to my grandma. However I can live with it, and indeed I use it as my main wallet.