ProphetSword
Explorer
I've had multi-classing in all three of my campaigns, and to date it hasn't broken anything. Actually, players rarely seem to bother with multi-classing in this edition; because single-class characters seem stronger.
A lot of people will give nuanced takes on the capabilities of your players and the table's desires for the type of game they want to play.
I'm going to part from that and just say "multiclass is trash."
-Brad
Multiclassing is not an issue for me, it helps shore up holes in small parties, case in point our party has Tabaxi monk, goblin fighter, tabaxi fighter, firbolg ranger and lizardfolk barbarian, we are short on healing so the goblin is mc'ing into life cleric for a few levels, without that option it would make it much tougher.
To fulfill Character Concept--'nuff said. It's that easy. Don't worry about "power-balance"--it's a fraud. Any DM worth their salt should encourage their players to make the PC's that they want to make. Self-imposed limitations, even in the vein of good intentions, are STILL limitations...in a nutshell: if it's good enough to be published by WotC (5E) in what limited capacity they're currently publishing, there simply has to be some merit to that.